Amol Choudhary

Diode-pumped femtosecond solid-state waveguide laser with a 4.9 GHz pulse repetition rate

We report on the first demonstration of a passively mode-locked, diode-pumped, monolithic Yb:glass channel waveguide laser that incorporates a semiconductor saturable absorber mirror. Stable and self-starting mode-locking is achieved in a Fabry-Perot cavity configuration producing a pulse repetition rate up to 4.9 GHz. The shortest pulse duration of 740 fs is generated with 30 mW of average output power at a center wavelength of 1058 nm. A maximum output power of 81 mW is produced during mode-locking with corresponding pulse duration of 800 fs.

Efficient frequency shifting of dispersive waves at solitons

We demonstrate frequency redshifting and blueshifting of dispersive waves at group velocity horizons of solitons in fibers. The tunnelling probability of waves that cannot propagate through the fiber-optical solitons (horizons) is measured and described analytically. For shifts up to two times the soliton spectral width, the waves frequency shift with probability exceeding 90% rather than tunnelling through the soliton in our experiment. We also discuss key features of fiber optical Cherenkov radiation such as high efficiency and large bandwidth within this framework.

Tailoring of the Brillouin gain for on-chip widely tunable and reconfigurable broadband microwave photonic filters

An unprecedented Brillouin gain of 44 dB in a photonic chip enables the realization of broadly tunable and reconfigurable integrated microwave photonic filters. More than a decade bandwidth reconfigurability from 30 up to 440 MHz, with a passband ripple <1.9  dB is achieved by tailoring the Brillouin pump. The filter central frequency is continuously tuned up to 30 GHz with no degradation of the passband response, which is a major improvement over electronic filters. Furthermore, we demonstrate pump tailoring to realize multiple bandpass filters with different bandwidths and central frequencies, paving the way for multiple on-chip microwave filters and channelizers.

Fundamentally mode-locked, femtosecond waveguide oscillators with multi-gigahertz repetition frequencies up to 15 GHz

We demonstrate passively mode-locked Yb(3+)-doped glass waveguide lasers in a quasi-monolithic configuration with a maximum pulse repetition frequency up to 15.2 GHz. A semiconductor saturable absorber mirror (SESAM) is used to achieve stable mode-locking around 1050 nm with pulse durations as short as 811 fs and an average power up to 27 mW. Different waveguide samples are also employed to deliver pulses with repetition rates of 4.9 GHz, 10.4 GHz and 12 GHz with an average power of 32 mW, 60 mW and 45 mW, respectively. The group velocity dispersion control in the cavity is provided by changing the gap between the SESAM and the waveguide end-face to facilitate a soliton mode-locking regime.

Graphene Q-Switched Mode-Locked and Q-Switched Ion-Exchanged Waveguide Lasers

In this letter, we present the use of monolayer graphene saturable absorbers to produce Q-switched and Q-switched mode-locked operation of Yb and Yb:Er-doped phosphate glass waveguide lasers, respectively. For the 1535-nm-wavelength Yb:Er laser, the Q-switched pulses have repetition rates up to 526 kHz and contain mode-locked pulses at a repetition frequency of 6.8 GHz. The measured 0.44-nm bandwidth should allow pulses as short as ~6 ps to be generated. Maximum average output powers of 27 mW are obtained at a slope efficiency of 5% in this mode of operation. For the 1057-nm-wavelength Yb laser, Q-switched pulses are obtained with a repetition rate of up to 833 kHz and a maximum average output power of 21 mW. The pulse duration is found to decrease from 292 to 140 ns and the pulse energy increase from 17 to 27 nJ as the incident pump power increases from 220 to 652 mW.

Q-switched operation of a pulsed-laser-deposited Yb:Y 2 O 3 waveguide using graphene as a saturable absorber

The first, to the best of our knowledge, Q-switched operation of a pulsed-laser-deposited waveguide laser is presented. A clad Yb:Y(2)O(3) waveguide was Q-switched using an output coupling mirror coated with a single layer of graphene deposited by atmospheric pressure chemical vapor deposition. During continuous-wave operation, a maximum power of 83 mW at a slope efficiency of 25% was obtained. During Q-switched operation, pulses as short as 98 ns were obtained at a repetition rate of 1.04 MHz and a central wavelength of 1030.8 nm.

456-mW graphene Q-switched Yb:yttria waveguide laser by evanescent-field interaction.

In this Letter, we present a passively Q-switched Yb:Y2O3 waveguide laser using evanescent-field interaction with an atmospheric-pressure-chemical-vapor-deposited graphene saturable absorber. The waveguide, pumped by a broad area diode laser, produced an average output power of 456 mW at an absorbed power of 4.1 W. The corresponding pulse energy and peak power were 330 nJ and 2 W, respectively. No graphene damage was observed, demonstrating the suitability of top-deposited graphene for high-power operation.

Advanced Integrated Microwave Signal Processing With Giant On-Chip Brillouin Gain

Processing of microwave signals using photonics has several key advantages for applications in wireless communications. However, to bring photonic-based microwave signal processing to the mainstream requires a reduction of the form factor. Integration is a route for achieving high-performance, low-cost, and small-footprint microwave photonic devices. A high on-chip stimulated Brillouin scattering (SBS) gain is essential for synthesizing several key functionalities for advanced integrated microwave signal processing. We have optimized our on-chip SBS platform to achieve a record on-chip gain of 52 dB. In this paper, we discuss the implications of this giant gain from the viewpoint of new enabled technologies. The giant gain can be distributed over wide frequencies, which can be exploited for the realization of reconfigurable microwave bandpass, bandstop, and multiband filters. High gain also enables the demonstration of low-threshold on-chip lasers, which can be of relevance for a low-noise radio-frequency signal generation. These wide ranges of functionalities are made possible by the breakthrough on-chip gain makes Brillouin-based microwave photonic signal processing a promising approach for real-world implementation in the near future.

Ion-exchanged Tm3+:glass channel waveguide laser

Continuous wave laser action around 1.9 μm has been demonstrated in a Tm(3+)-doped germanate glass channel waveguide laser fabricated by ion-exchange. Laser action was observed with an absorbed power threshold of only 44 mW and a slope efficiency of up to 6.8% was achieved. Propagation loss at the lasing wavelength was measured to be 0.3 dB/cm. We believe this to be the first ion-exchanged Tm(3+)-doped glass waveguide laser.

A diode-pumped 1.5 μm waveguide laser mode-locked at 6.8 GHz by a quantum dot SESAM

We report a passively mode-locked, diode-pumped waveguide laser operating in the 1.5µm spectral region using a quantum dot SESAM as the saturable absorber element. A repetition rate of up to 6.8GHz and an average power as high as 30mW is obtained during mode-locked operation. Minimum pulse duration of 2.5ps is produced at a wavelength of 1556nm. The repetition rate of the source was tuned by more than 1 MHz by changing the pump power, demonstrating a possible route towards integrated pulse repetition rate stabilisation.