Fibre-optic digital transmission experiment with heterodyne detection

A single-channel single-polarisation all-fibre-optic transmission system at 830 nm wavelength with transmitter laser and a heterodyne receiver with local laser, monomode fibre coupler and APD mixer has been set up. The intermediate frequency was 1.5 GHz. 8.4 Mbit/s digital signals were transmitted over 280 m of single-polarisation fibre by a subcarrier modulated baseband method.     

Fabrication of single-polarisation single-mode-fibre couplers

Fused biconical taper fibre couplers have been fabricated from single-polarisation single-mode fibres. A CVD technique is applied to permit maintenance of parallel alignment of the fibres in the coupler fabrication process. The couplers can hold linear polarisation along the principal axis of the fibre branches, showing an extinction ratio of about ?15dB.     

Polarising fibre coupler with high extinction ratio

Fused polarising fibre couplers have been fabricated using single-polarisation single-mode fibres. When circularly polarised light is fed into the coupler, one of the two orthogonal polarisation modes suffers strong attenuation, and only one polarisation mode couples in the fused biconical taper region. The extinction ratio of the coupler is 41 dB at a wavelength ? = 1.3 ?m with a coupling ratio of 48:52.     

Polarisation preserving single-mode-fibre coupler

A polarisation-preserving single-mode-fibre coupler made by an etch-fusion technique with Hitachi single-polarisation fibre is reported. Polarisation isolation of 10?20 dB is typically maintained through the coupler. Power division of ? 45?55% is achieved with an excess loss of 0.2 dB.     

3 km-long single-polarisation single-mode fibre

A single-polarisation single-mode (SPSM) fibre with crosstalk of ?40 dB in a 3.2 km length has been demonstrated. No crosstalk degradation was found for lengths of more than 0.2 km. The two polarisations of the fundamental mode were split with a high modal birefringence of 8.5×10?4, which was produced by PANDA structure. The transmission loss was 2.8 dB/km at 1.56 ?m.     

High-efficiency, single-longitudinal-mode ring fibre laser

A novel single-longitudinal-mode erbium-doped ring fibre laser is proposed and demonstrated experimentally. It combines a narrow-linewidth fibre Bragg grating (FBG) with several Mach-Zehnder mode filters (MZF) to obtain a single-frequency emission. It yields a power conversion efficiency of 16%. It is shown that the sidemodes are suppressed when one inserts the series of MZFs inside the cavity. At 1547 nm, the output power measures over 15 dBm, with a sidemode suppression ratio of 50 dB and a linewidth of no more than 7 kHz.     

Tunable single-mode output of a multimode laser in a tunable fibre grating external cavity

Tunable single-mode oscillation has been obtained from a 1.3?m multimode laser using a tunable fibre grating reflector in a fibre external cavity. The output was tuned over a 26 nm range with a secondary mode suppression greater than 25 dB at the centre of the gain profile.     

Stabilisation of a modelocked Er-doped fibre laser by suppressingthe relaxation oscillation frequency component

A novel method is reported for stabilising an actively modelocked Er-doped fibre laser by controlling its cavity length to suppress the relaxation oscillation RF power of the laser output. This RF power is a good measure of laser instability. With this method, the RF power ratio between modelocking frequency and background noise is kept to more than 70 dB, and stable bit-error-free operation at 6.3 GHz is realised for over 6 hr     

1.5 mu m GaInAsP/InP distributed reflector (DR) laser with high-low reflection grating structure

A 1.5 mu m-wavelength dynamic-single-mode laser with high-low reflection grating structure aiming at high output and uni-directional output operation has been obtained for the first time using a selective etching process and low-pressure MOVPE regrowth. A front/rear output power ratio exceeding 50 and side-mode suppression ratio (SMSR) greater than 39 dB were obtained at 1.3 times the threshold.<>     

Six-wavelength Raman fibre laser for C- and L-band Ramanamplification and dynamic gain flattening

A novel six-wavelength Raman fibre laser exhibiting a dynamic gain flattening capability in the C + L optical telecommunications band is demonstrated. The power distribution in the six lasing wavelengths is adjusted with voltage-controlled Bragg-grating output couplers. The fibre laser was used as a pump source for distributed Raman amplification in several transmission span lengths. For example, the multiwavelength laser provides an on/off gain of 19 dB over a 100 km span of True-Wave RS optical fibre. The measured gain flatness is 1.7 dB peak-peak and the effective noise figure ranges from 1.6 to -5.2 dB in the 1530 to 1600 nm bandwidth     

Dual-Frequency Operation in a Short-Cavity Ytterbium-Doped Fiber Laser

A dual-frequency 2-cm silica fiber laser with a wavelength spacing of 0.3 nm has been demonstrated using a polarization-maintaining (PM) fiber-Bragg-grating (FBG) reflector. The birefringence of the PM FBG was used to generate the two single-mode (SM) lasing frequencies of orthogonal polarizations. The SM operation in each wavelength has been verified. The output power reaches 43 mW with the optical signal-to-noise ratio of greater than 60 dB. The fiber laser shows stable dual-frequency output under pump variations     

80 nm spectrally flattened, high power erbium amplified spontaneousemission fibre source

A novel two-stage spectrally flattened, high output power erbium amplified spontaneous emission (ASE) fibre source pumped using a single laser diode pump is reported. The source has a bandwidth of 80 nm with a 1 dB ripple and output power of +13 dBm (20 mW)     

基于M-Z滤波的波长可调谐掺铒光纤随机激光器

提出了一种基于M-Z结构的可调谐掺铒光纤随机激光器,并对随机激光输出过程、随机激光的波长可调谐输出以及随机激光的稳定性进行了实验研究。通过采用光纤熔接手段将两个2×2光纤耦合器进行熔接,构成全光纤M-Z滤波结构。实验结果表明,激光器的阈值功率为120mW,调整可调谐衰减器改变增益损耗,实现波长可调谐输出,其中单波长输出分别为1554.4,1555.2和1556.3nm,信噪比达到31.65dB;双波长输出分别为1525.9,1556.2和1531.6,1556.2nm,信噪比优于21.92dB;三波长输出分别为1527.4,1546.9,1551.6和1526.9,1530.0,1549.8nm,信噪比优于20.10dB;四波长输出为1525.9,1530.1,1547.9和1552.3nm,信噪比优于18.95dB;其中单波长和双波长的功率波动分别优于1.65和1.99dB;激光器斜率效率为0.627%。     

A widely tunable SOA-integrated DBR laser by combination of sampled and superstructure gratings

We report on the development of the first 30 nm tunable laser diode utilizing a front sampled grating-distributed Bragg reflector (SG-DBR) and a rear superstructure grating DBR (SSG-DBR). A high output power greater than 18 mW was achieved with superior longitudinal mode stability, as well as an overall power variation of less than 3 dB for the well-defined laser. Furthermore, lasers integrated with a semiconductor optical amplifier (SOA) enabled the output power to be controlled independently both by the active current and the SOA current, as well as achieving a maximum output power of 45 mW. The side-mode suppression ratio was in excess of 40 dB for all the 50 GHz spaced wavelength channels.     

L-band erbium-doped fibre amplifier with clamped- and flattened-gain using FBG

A gain clamped long wavelength band erbium-doped fibre amplifier (L-band EDFA) based on a ring laser cavity is demonstrated using a fibre Bragg grating (FBG) at the output end of the amplifier. This new design provides a good gain clamping as well as a gain flattening. The gain is clamped at 16.9 dB with gain variation of less than 0.1 dB from input signal power of -40 to -18 dBm by setting the VOA=5 dB. Also, the amplifier has the flattest gain spectrum at VOA=5. The gain variation is less than 1.0 dB within the wavelength range from 1570 to 1600 nm. This gain clamped amplifier also can support a 12 channel WDM system.     

Highly Narrow Linewidth, CW, All-Fiber Oscillator With a Switchable Linear Polarization

We present a fiber laser with a switchable state of linearly polarized output realized by inscribing point-by-point fiber Bragg gratings directly into the active core of a polarization-maintaining fiber. The compact all-fiber system exhibited a very narrow laser linewidth of ~13.5 pm (3.5 GHz), at a maximum continuous-wave output power of 188 mW. The optical signal-to-noise ratio was greater then 62 dB for both lasing polarizations. The robust system exhibited excellent long-term wavelength and laser linewidth stability.     

Monolithic digital supermode distributed Bragg reflector laser with record tuned ex-facet power in excess of 20dBm over C-band

An improved digital supermode distributed Bragg reflector laser with a monolithically integrated semiconductor optical amplifier with ex-facet output powers greater than 20 dBm over the full C-band is reported. In addition, the sidemode suppression ratio was greater than 40 dB over the full timing range.     

基于马赫-曾德尔干涉仪的可调谐掺镱光纤激光器

A ring-shaped all fiber tunable Yb-doped fiber laser with tuning range over 20 nm is demonstrated by using a fiber Mach-Zenhder interferometer as an intra-cavity filter which is constructed with two 3-dB optical couplers. The method for fabricating the fiber Mach-Zenhder interferometer is detailed. The fiber laser has a moderate milli-Watt level output power over the whole tuning range from 1050 to 1071 nm, a side-band suppression ratio greater than 45 dB, and a bandwidth less than 0.1 nm.     

35 AM-VSB TV channels distribution with high signal quality using a1480 nm diode-pumped erbium-doped fiber postamplifier

In the system considered, the postamplifier, with an output power of +9.6 dBm, did not degrade the very high linearity of the isolated distributed-feedback (DFB) laser transmitter. A 51.2-dB weighted signal-to-noise ratio was obtained, and an optical power budget of 16 dB was achieved with a weighted signal-to-noise ratio higher than 48 dB. A larger power budget with a higher signal-to-noise ratio (SNR) is possible with an increase of DFB laser output power and erbium-doped fiber amplifier (EDFA) saturated output power, and with a minimization of the EDFA noise contribution     

Optical time-division multiplexed transmission at 8 Gbit/s using single laser and semiconductor optical power amplifier

The authors report transmission over 57 km of single-mode fibre in a two-channel, 8 Gbit/s optical time-division multiplexed system experiment using a transmitter with a single laser and a semiconductor optical power amplifier at the transmitter output. The amplifier operates with a net gain of 11.5 dB, which corresponds to 0.8 dB gain compression, and a fibre coupled output power of +6 dBm. The amplifier facet output power for which the gain is compressed by 3 dB is +13 dBm. The experimental system uses neither an isolator nor an optical filter.<>