Bikash Nakarmi

The Development of an

Phase sensitive optical time domain reflectometry is suitable for vibration detection due to its high sensitivity. However, for conventional amplitude-measuring method, the strain-amplitude relation is nonlinear and the monotonic interval of strain-amplitude transfer function is very small (corresponding to less than 2π phase shift in light duration). Thus, the vibration detection is qualitative and it is difficult to distinguish different kinds of vibrations. In this letter, a quantitative vibration measurement by analyzing the differential phase in the interrogated fiber separation is proposed. A statistics calculating method is present to suppress the uncertainty in phase-measuring. Dynamic strain of 400 nε (peak-to-peak, corresponding to phase shift of 17 rad) was reproduced with high quality by proposed method.

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A two-bit all-optical digital comparator using single mode Fabry-Pérot laser diodes (SMFP-LDs) at an input data rate of 10 Gbps is proposed and demonstrated. All-optical comparator is demonstrated using cascaded logic units which are based on injection locking, multi-input injection locking and supporting beam principles for suppressing the dominant mode of SMFP-LDs. Digital comparators are the key components for the decision making circuits, the integral part of the arithmetic and logical units of optical data processors. The output performance of the proposed all-optical comparator is verified with output waveform, rising-falling time, output eye diagram, and bit error rate (BER) at 10 Gbps input Non Return to Zero (NRZ) PRBS of 231-1 signal. The rising/falling time of about 47 ps, clear output waveforms, and clear output eye diagram with an extinction ratio of about 12 dB are obtained. A maximum power penalty of 1.3 dB is measured at a BER of 10-9.

-OTDR System for Quantitative Vibration Measurement

A novel, simple, and universal all-optical NAND gate using single-mode Fabry-Pérot laser diode (SMFP-LD) is demonstrated. The basic operating principle of the proposed NAND gate is the modulation of the dominant lasing mode of SMFP-LD by the injection of external beams. The dominant lasing mode gain is suppressed only when both input beams are high. As SMFP-LD is used to demonstrate the logic function, no additional beam is required as needed in the multimode Fabry-Pérot laser diode (MMFP-LD) schemes. The operating principle is explained and the experimental results are presented at 10 Gb/s input data. The logic function is realized with a clear eye opening and an extinction ratio of 14.6 dB with a rising and falling time of 38.3 and 67.1 ps, respectively.

Realization of All-Optical Digital Comparator Using Single Mode Fabry–Pérot Laser Diodes

We propose a novel idea for the suppression of the dominant mode of the single-mode Fabry-Pérot laser diode (SMFP-LD) to realize all-optical multi-logic functions and a digital adder. The basic principle of the proposed scheme is the power management of input beams to suppress the dominant mode of the SMFP-LD for multi-input injection locking. The proposed principle is explained and implemented to realize all-optical multi-logic functions and a digital adder at an input data rate of 10 Gbps. A clear eye opening with an extinction ratio of about 12 dB and a rising-falling time of less than 40 ps are observed at the outputs. The bit error rate (BER) performance is measured for all logic gates and half adder operation. We found there is no BER floor up to BER of 10(-12) and the maximum power penalty of about 1.2 dB at a BER of 10(-9).

Demonstration of All-Optical nand Gate Using Single-Mode Fabry–Pérot Laser Diode

A novel and simple controlled all-optical on/off switch using the gain modulation in a single-mode Fabry-Pérot laser diode (SMFP-LD) is demonstrated. The working principle of the proposed on/off switch is explained and the experimental results with 10 Gb/s data signal are presented. The 10 Gb/s data signal is switched on and off with a 350 MHz control signal. The extinction ratio of 15.6 dB is observed at the output port with a 2 dB power difference between the control signal and input signal. We measured the rising and falling time of the switch output as 48 and 59 ps, respectively.

Realization of all-optical multi-logic functions and a digital adder with input beam power management for multi-input injection locking in a single-mode Fabry-Pérot laser diode

We propose and demonstrate a novel scheme for short pulse controlled all-optical switch using external cavity based single mode Fabry- Pérot laser diode (SMFP-LD). The proposed scheme consists of control unit and switching unit as two essential blocks. The basic principle of the proposed scheme is the optical bistability property of SMFP-LD for the control unit and the suppression of the dominant beam of SMFP-LD with injection locking for the switching unit. We also present the analysis of hysteresis width and rising/falling time with change in wavelength detuning which helps to find the optimum wavelength detuning value and power of light beams at different stages of the proposed scheme that gives wide input dynamic power range, high ON/OFF contrast ratio, and low rising/falling time. Input data of 10 Gb/s Non Return to Zero (NRZ) signal is switched at output ports depending upon the control signal generated by the control unit, which comprises of optical SR latch. Output waveforms, clear eye diagrams with extinction ratio of about 11 dB, rising/falling time of about 30 ps and 40 ps, and bit error rate (BER) are measured to validate proposed scheme. No noise floor is observed at output ports up to BER of 10-(12) and the maximum power penalty recorded is about 1.7 dB at a BER of 10-(9) which shows good performance of the proposed short pulse controlled optical switch using SMFP-LDs.

A Simple Controlled All-Optical on/off Switch Using Gain Modulation in Single Mode FP-LD

In this paper, we use optical feedback injection technique to generate tunable microwave, millimeter-wave and submillimeter-wave signals using single-mode Fabry-Pérot laser diode. The beat frequency of the proposed generator ranges from 30.4 GHz to 3.40 THz. The peak power ratio between two resonating modes at the output spectrum of can be less than 0.5 dB by judiciously selecting feedback wavelength. In the stabilization test, the peak fluctuation of photonic signal is as low as 0.19 dB within half hour. Aside from locking regions, where the laser is easily locked by the injection beam, the side-mode suppression ratio is well over 25 dB with the maximum value of 36.6 dB at 30.4 GHz beat frequency. In addition, the minimum beat frequency interval between two adjacent photonic signals is as low as 10 GHz.

Short-pulse controlled optical switch using external cavity based single mode Fabry-Pérot laser diode.

The width of hysteresis in optical bistability plays an important role on latching operation. The injected input optical power and wavelength detuning in single mode Fabry-Perot laser diode (SMFP-LD) are two parameters that can impact the width of hysteresis in bistability of dominant mode and injected mode. In this paper, we analyze the effect of wavelength detuning on width of the hysteresis loop, the dynamic power range for optical bistability, and the rising-falling time of output waveform. With this analysis, optical Set Reset flip-flop with simultaneous inverted and non-inverted output at the data rate of 8.5 Gb/s are obtained using SMFP-LDs. The principle is based on the optical bistability phenomena during injection-locking of the Fabry-Perot laser diode. The set and reset pulses are maintained in low power of about -14 and -6 dBm for the power effective configuration. The contrast ratios of more than 20 dB with simultaneous non-inverted and inverted output Q and Q are observed. Clear output spectrum domain results, waveforms, eye diagram with extinction ratio of more than 12 dB, a rising/falling time of about 40 ps, and bit error rate (BER) measurement without noise floor up to 10 -12 are observed. The maximum power penalty is about 1.8 dB at BER of 10 -9.

Optically tunable microwave, millimeter-wave and submillimeter-wave utilizing single-mode Fabry-Pérot laser diode subject to optical feedback.

In this paper, optical bistability characteristics are demonstrated experimentally based on a dual-mode laser system comprising a multi-mode Fabry-Perot laser diode (MMFP-LD) and a built-in feedback cavity formed by a fiber facet. The results show that two lasing modes with frequency separation of ∼0.58 THz and comparable peak powers can be achieved by judicious adjustment of the bias current and the operating temperature of the laser chip, which has a peak fluctuation of less than ∼1 dBm over a measurement period of one hour. A combination of appropriate external injection power and wavelength detuning can result in remarkable optical bistability in two oscillation modes, in which the resulting contrast ratio between the unlocked and locked states can be up to 30 dB, and the corresponding hysteresis loop width can be changed by controlling the side-mode injection power and the wavelength detuning.

Analysis of Hysteresis Width on Optical Bistability for the Realization of Optical SR Flip-Flop Using SMFP-LDs With Simultaneous Inverted and Non-Inverted Outputs

All-optical two bit digital comparator using single mode Fabry-Perot laser diodes (SMFP-LDs) is proposed and demonstrated with 10 Gbps PRBS signal of 231-1. Digital comparators are one of the important components for decision making circuits, threshold detection, which are used in optical signal processing and optical computing. The basic principle of the comparator is based on injection locking, multi-input injection locking and combinational input injection locking (CMIL) to realize the greater than, less than, and equal to function of the basic comparator circuit. These principles are used to realize the different optical logic gates which are combined together to demonstrate optical comparator with the minimum number of components, making the configuration cheaper and simpler. The proposed method draws less current and hence power effective too. Output waveform diagram and output eye diagram for all three cases of comparator are presented to verify all functions of all-optical comparator.