Birefringent Filter Research Articles

Dual-parameter demodulated torsion sensor based on the Lyot filter with a twisted polarization-maintaining fiber.

We proposed a novel torsion sensor based on the Lyot filter with the twisted polarization-maintaining fiber (PMF) acting as the birefringence medium. Lyot filter is formed by two linear polarizers and a piece of PMF. Based on the high birefringence of the PMF, the output polarization rotates with a rate equal to the twisting rate applied on the PMF, and the sensor realizes a high sensitivity of 90.072 dB/rad. The proposed sensor also demonstrated a low strain sensitivity of 2.32 ×10 - 6 rad/μɛ. On the other hand, based on the phase hits of the polarization interference, the wavelength sensitivity reaches 15.477 nm/rad. The monitoring range of the wavelength demodulation is complementary with the intensity demodulation in one cycle, making the valid sensing range of the proposed sensor expand. The proposed highly sensitive compact torsion sensor, with large sensing range and low crosstalk, has potential applications in many fields such as manufacturing industry, civil engineering, aerospace industry and modern smart structure monitoring.

Frequency-tunable optical fiber passband-squeezed birefringence filter based on quarter-wave polarization conversion

A polarization-diversified loop structure (PDLS) formed by a four-port polarizing beam splitter has been employed to establish the input polarization independence of optical devices. Here we report a PDLS-based optical fiber birefringence filter, which can provide continuous frequency tunability in passband-squeezed comb spectra by harnessing quarter-wave polarization conversion. The birefringence filter is composed of a four-port PBS, two high birefringence fiber (HBF) segments whose lengths are equal, the first polarization controller (PC) comprised of a quarter-wave retarder (QWR) and a half-wave retarder (HWR), which is located in front of the first HBF segment, and a set of two QWRs as the second PC that lies before the second HBF segment. The dual QWRs, chosen for the second PC, are the simplest form of a PC that can convert arbitrary input polarization into desired polarization. The slow axis of the second HBF segment is oriented at 22.5° with respect to the horizontal axis of the PBS. Through the Jones matrix formulation, we derived the sinusoidal passband-squeezed transmittance function of the filter, whose absolute phase (ϕ) should be continuously varied for the contiguous wavelength tuning of filter spectra. Then, using this filter transmittance, we found the possible loci of the orientation angles (OAs) of the four wave retarders as the functions of ϕ. By utilizing the OA loci of the wave retarders, the theoretical passband-squeezed transmission spectra of the filter were calculated for eight equally spaced values of ϕ from 0° to 315° (with an increment of 45°). This theoretical calculation was also verified by measuring the wavelength-tuned passband-squeezed spectra of the fabricated filter. We theoretically and experimentally confirmed that our filter could provide the wavelength tunability of the polarization-independent passband-squeezed comb spectrum by appropriately controlling the OAs of the wave retarders.

Birefringence, isotropic points, and optical filters based on CuGaxAl1-xSe(S)2 crystals

A brief review on birefringence and optical filters based on CuGaxAl1-xS2 and CuGaxAl1-xSe2 crystals is given in this paper. Two types of isotropic points are analyzed; one of them refers to a case when the wavelength at which the ordinary and extraordinary refractive indices are equal is situated near the absorption edge, while in the second case the isotropic wavelength is in the region of crystal transparency. It is shown that both of them can be used for the development of band-pass and band-reject filters. The possibility of adjusting the spectral position of an isotropic point by changing the chemical composition of a solid solution is illustrated, and the applicability of CuGaxAl1-xS2 and CuGaxAl1-xSe2 for adjusting the isotropic point to most of Ar+, Kr+, He–Ne, and He–Cd gas lasers lines, as well as to semiconductor lasers, is revealed

High-energy broadband Nd: Glass regenerative amplifier with coated birefringent filter for the high-power laser facilities

The regenerative amplifier is an important component of the high-power laser facility. A high-energy broadband Nd: glass regenerative amplifier with an energy of 34.1 mJ and a bandwidth of 4.3 nm was demonstrated using an intra-cavity specially coated birefringent filter (CBRF). This letter proposes a design scheme for a CBRF that can control the flat-top area of gain spectrum of the regenerative amplifier, which has been studied theoretically and experimentally. The transmittance of the specially coated BRF was tested in this experiment. The amplifier output spectrum had a flexible control ability and long-term stability. It can be applied to support high-energy broadband amplification in inertial confinement fusion (ICF) facilities, and can also be extended to other broadband amplification system to support high-energy picosecond petawatt laser facilities.

Low threshold multi-wavelength erbium-doped fiber ring laser with NOLM and Lyot filter

In this paper, the performance of a switchable multi-wavelength erbium-doped fiber laser (MWEDFL) incorporating Lyot filter and nonlinear optical loop mirror (NOLM) is described. The NOLM consisting of a polarization controller (PC2) and a single-mode fiber is effective to suppress the mode competition caused by the homogeneous broaden line in the erbium-doped fiber amplifier (EDFA). The comb filter is developed by using PC1 and polarization-maintained fiber (PMF). The wavelength interval can be switched among 0.08 nm, 0.34 nm, and 0.89 nm using different lengths of PMF via careful adjusting of the PCs. When the pump power is 45mW, the laser can emit 12 stable lasing lines within the 3 dB bandwidth, and the side mode suppression ratio (SMSR) is greater than 25 dB. The spectral power and wavelength fluctuations of 1.9 dB and 0.16 nm, respectively. Experimental results reveal that the demonstrated laser has good stability and low threshold power.

Widely Tunable Narrow-Linewidth Intracavity Optical Parametric Oscillators Based on an Yb: KYW Laser

We report the generation of widely-tunable, narrow-linewidth midinfrared laser emission from an Yb: KYW-based intracavity singly-resonant optical parametric oscillator (ICSRO). The wavelength-tuning scheme is based on exploiting the wide emission-bandwidth of Yb: KYW crystals. Birefringent filters were used in the ICSRO cavity for linewidth narrowing and wavelength tuning. The benefit of this tuning scheme is that it does not rely on the temperature-tuning mechanism or the usage of customized fanout PPLN crystals. By using 6 different poling-periods of a 25 mm-long PPLN crystal, and synchronizing the tuning of the pump and signal waves, we obtained midinfrared idler light with a tuning range over 2600–4030 nm, having an estimated linewidth of less than 0.8 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> .

Mode-locked Cr:LiSAF laser far off the gain peak: tunable sub-200-fs pulses near 1 µm.

We report, to the best of our knowledge, the first mode-locking results of a Cr:LiSAF laser near the 1 µm region. The system is pumped only by a single 1.1 W high-brightness tapered diode laser at 675 nm. A semiconductor saturable absorber mirror (SESAM) with a modulation depth of 1.5% and non-saturable losses below 0.5% was used for mode-locking. Once mode-locked, the Cr:LiSAF laser produced almost-transform-limited sub-200-fs pulses with up to 12.5 mW of average power at a repetition rate of 150 MHz. Using an intracavity birefringent filter, the central wavelength of the pulses could be smoothly tuned in the 1000-1020 nm range. Via careful dispersion optimization, pulse widths could be reduced down to the 110-fs level. The performance in this initial study was limited by the design parameters of the SESAM used, especially its passive losses and could be improved with an optimized SESAM design.

Theoretical study on the effectiveness of optical filters to suppress orientation-based solar light noise.

It is well established in the literature that the performance of an underwater optical wireless communication (UOWC) system degrades due to various channel-based and environmental attributes. So far, consistent performance by a UOWC system has not been discussed when the system receiver (Rx) is positioned at a certain depth and takes on different orientations, i.e., vertically upward or downward, and horizontally left or right. This paper discusses the UOWC system performance when the Rx points in three different orientations and captures the modulated light signal and different intensities of solar light. We carry out a detailed comparative performance analysis of the UOWC Rx system considering various optical components, such as a colored glass optical bandpass filter, optical thin-film interference filter, and optical wide-field birefringent filter (OWFBF), which are mounted in front of the UOWC Rx to suppress solar light noise interference for different orientations. We observe that the same UOWC Rx behaves differently in all three orientations and the OWFBF outperforms.

Wavelength-Tunable L-Band High Repetition Rate Erbium-Doped Fiber Laser Based on Dissipative Four-Wave Mixing.

A wavelength-tunable high repetition rate (HRR) erbium-doped fiber laser in L-band based on dissipative four-wave mixing (DFWM) mechanism is demonstrated. The cavity can generate a single-soliton train and bound-soliton train with a fixed repetition rate of ~126 GHz, which is determined by the free spectral range of the intra-cavity Lyot filter. A wide wavelength-tuning operation can also be obtained by rotating the polarization controllers. The wavelength-tuning ranges of the HRR single-soliton state and HRR bound-soliton state are ~38.3 nm and ~22.6 nm, respectively. This laser provides useful references for the area of a wavelength-tunable fiber laser with high repetition rate. The laser may also find useful applications in high-speed communication, sensing, etc.

Highly Birefringent Microfiber Hybrid Interferometer Sensor

In this work, an optical microfiber-based hybrid interferometer is presented. A combination of two types of in-line interferometers is achieved by inserting a section of nonadiabatic tapered polarization maintaining microfiber into a Lyot filter. The hybrid interference spectrum shown as large spectrum envelope and fine fringes, corresponding to the polarized and modal interferences is obtained. We experimentally investigate the response characteristics of the two-interference system using both spectral interrogation and spatial frequency domain analysis. The refractive index sensitivities are 1150.0nm/RIU and 1779.8nm/RIU, and the temperature sensitivities are 190pm/°C and -12.7 pm/°C for two interferences, respectively. The proposed hybrid interferometer has the advantages of simple device and compact structure, and has the potential of simultaneous measurement of multiple parameters.

Wavelength switchable dissipative soliton mode-locked fiber laser based on Lyot filter

We propose a wavelength switchable mode-locked fiber laser based on a homemade fiber Lyot filter that is comprised of 18-cm-long polarization maintain fiber, polarizer, and polarization controller. The generation of mode-locked operation originates from the principle of NPR by the specific setup of PC + ISO + PMF and polarizer. Due to the Lyot filter, the central wavelength of mode-locked laser can be switched between 1036.6 nm and 1050.5 nm by modulating the polarization state of polarization controller and pump power. The switchable wavelength intervals were about 13.9 nm. Such a switchable mode-locked fiber laser has various potential applications in pulse fiber laser system.

The passband integration properties of Birefringent filter

In this article, we discuss an observation phenomenon where the total amount of photons in the full passband of the Birefringent filter is a constant number that is considered by removing the spectrum of the light source irrespective of the instrument transmittance. This conclusion is only noticed and considered to be correct in Huairou Solar Observing Station since 1980’s. This article will give a further discussion to the question that had been proposed by the previous researchers. The article structure is organized as history (Sec. 1), experiment (Sec. 2), math (Sec. 3), and discussion (Sec. 4). This issue should be the Paseval-Theorem manifesting itself in astronomical measurement, even though we rigorously demonstrate that this photons conservation has its mathematical generality in Sec. 3.

Design of a narrow band-pass birefringent filter for visible range

Design of a narrow band-pass birefringent filter for visible range

All-solid-state widely wavelength-tunable and high-efficiency Yb:YSr3(PO4)3 laser.

We demonstrate an all-solid-state widely wavelength-tunable Yb:YSr3(PO4)3 (Yb:YSP) laser with high efficiency. The free-running Yb:YSP laser oscillating at multiple wavelengths in the range of 1024-1054 nm is realized with different crystal lengths and output coupler transmittances. The maximum output power of 2.72 W is obtained under the absorption pump power of 7.30 W. The highest slope efficiency is 66.9%, using the crystal of 6.5-mm-length. Simultaneous dual-wavelength operation can be realized as well. Furthermore, the widely wavelength-tunable Yb:YSP laser with a range of more than 60 nm (from 1004 to 1066 nm) is achieved using a birefringent filter. The experimental results indicate that the Yb:YSP crystal can be a promising candidate for ultrafast lasers in the 1 µm region.

Widely tunable external-cavity surface-emitting laser using various methods.

We report a widely tunable optically pumped vertical-external-cavity surface-emitting laser. The multiple quantum wells in the active region of the gain chip are generally designed to form the resonant periodic gain structure, and three different methods are used to tune the oscillating wavelength. The maximum wavelength coverage of 45 nm is obtained when a 2 mm thickness birefringent filter is introduced in a straight-line cavity, while the tuning range of 8 nm is performed by employing a 0.15 mm thickness uncoated Fabry-Perot etalon. For the first time, to the best of our knowledge, we present an 11 nm tuning range by the use of an inserted blade as the tuning element, and the related wavelength tuning mechanism is analyzed.

Tunable continuous-wave dual-wavelength laser operation of Pr3+:LiYF4 around 900 nm

We present here the first tunable continuous-wave (CW) simultaneous dual-wavelength laser operation of a Pr3+:LiYF4 crystal in the 900 nm spectral range using a single birefringent filter (BF) under excitation with a frequency doubled optically pumped semiconductor laser. By adjusting the rotation angle of the BF, the CW simultaneous dual-wavelength lasers operating at 869 and 915 nm, 894 and 915 nm, 915 and 923 nm, were obtained respectively.

Tunable period-multiplying Q-switched pulse outputs based on birefringence induced multiwavelength tuning in a linear erbium-doped fiber oscillator

A tunable period-multiplying Q-switched erbium-doped fiber laser based on birefringence induced multiwavelength tuning in a linear cavity is demonstrated. By carefully adjusting the polarization controller to control birefringence filter effect under the pump power of 204 mW, period-doubling, period-tripling and period-quadrupling operations corresponding to dual-, quadruple- and triple-wavelength pulses are experimentally demonstrated, respectively. Unlike the traditional period-multiplying pulses operating in the narrow control parameters, they can persistently exist under constantly changing pump power from 204 mW to 117 mW. We attribute them to the intrinsic property of laser system with multiwavelength pulse emissions across 1530- and 1550-nm gain regions. And multiwavelength tuning provides the versatility of period-multiplying pulses. To the best of our knowledge, it is the first demonstration of the persistent and tunable period-multiplying Q-switched pulse outputs. This could offer an attractive alternative seed source integrated with all-optical modulation for applications requiring modulated Q-switched pulse sequences such as multiple-pulse laser-induced breakdown spectroscopy and processing.

Wavelength-tunable diamond Raman laser at ∼2.5 μm

We report on wavelength tunable operation of a diamond Raman laser at ∼2.5 μm pumped by a narrow linewidth Q-switched Tm:YAP laser at 1.88 μm. The Raman laser operates at 50 Hz of repetition rate and produced stable pulses of 1.12 mJ energy and 9.2 ns duration, corresponding to a peak power of ∼121.7 kW. Over 56 mW of average output power has been generated for ∼197 mW of incident pump power, corresponding to a slope efficiency of 45.3%. Output wavelength was tunable from 2511.1 nm to 2522.1 nm via a birefringence filter and two etalons incorporated in the Tm:YAP laser resonator.

편광 상이 고리 구조 내 복합 파장판 조합을 이용한 협대역 빗살 스펙트럼의 연속 파장 제어에 관한 연구

In this paper, we propose a novel birefringence filter based on polarization-diversity loop structure(PDLS) for continuous wavelength controlling of narrowband transmission spectrum. This filter consists of a polarization beam splitter(PBS), two high-birefringence fiber(HBF) of the same length, two half-wave plates(HWPs), and two quarter-wave plates(QWPs). We found a combination of the orientation angles of the four waveplates which could induce an additional phase difference φ from 0° to 360° to the narrowband transmittance function by considering the filter transmittance derived from Jones matrices. Then, we experimentally exhibited eight narrowband transmission spectra measured with a channel spacing of ∼0.1nm based on these theoretical calculations. As a result, we verified the effectiveness of the narrowband multiwavelength filter capable of continuously tuning its wavelength position when properly adjusting the combination of the orientation angles.

A tunable single-frequency green laser based on a wedged Nd:YVO4 crystal and a KTP crystal

A 532 nm single-frequency laser generated from a V-type oscillator configuration with a wedged Nd:YVO4 crystal and a KTP crystal is reported. An a-cut, 2.at% Nd:YVO4 crystal with a wedge angle of 10° and a KTP nonlinear crystal composes a novel birefringent filter. By adjusting the incident angle of the fundamental mode in the KTP, the laser can change from single-mode operation to two-mode oscillation. The maximum single-frequency output power of lasers with a 5 mm long KTP and a 7 mm long KTP are 284 and 148 mW, respectively, at pump powers of 2 and 1.1 W. The corresponding optical-to-optical conversion efficiencies are 14.2% and 13.5%. For the laser configuration with a 5 mm long KTP, the single-frequency operation at a pump power of 2 W is maintained within the temperature range of 18 °C to 24 °C, and the measured wavelength drift rate with the temperature is approximately 0.071 nm °C−1.