Lalitha Ponnampalam

Widely tunable DS-DBR laser with monolithically integrated SOA: design and performance

We report recent device characterization results for a fully packaged widely tunable digital supermode (DS) distributed Bragg reflector (DBR) laser which has been monolithically integrated with a semiconductor optical amplifier. This new device gives all of the wide tunability and high side-mode suppression ratio performance previously reported for the DS-DBR laser with the added feature of output powers in excess of 14 dBm in fiber. In addition to output power and basic tuning behavior, we report on linewidth and relative intensity noise measurements for this device in order to investigate the noise characteristics of this laser.

Millimeter-Wave Photonic Components for Broadband Wireless Systems

We report on advanced millimeter-wave (mm-wave) photonic components for broadband radio transmission. We have developed self-pulsating 60-GHz range quantum-dash Fabry-Perot mode-locked laser diodes (MLLD) for passive, i.e., unlocked, photonic mm-wave generation with comparably low-phase noise level of -76 dBc/Hz @ 100-kHz offset from a 58.8-GHz carrier. We further report on high-frequency 1.55-μm waveguide photodiodes (PD) with partially p-doped absorber for broadband operation (f3dB ~70-110 GHz) and peak output power levels up to +4.5 dBm @ 110 GHz as well as wideband antenna integrated photomixers for operation within 30-300 GHz and peak output power levels of -11 dBm @ 100 GHz and 6-mA photocurrent. We further present compact 60-GHz wireless transmitter and receiver modules for wireless transmission of uncompressed 1080p (2.97 Gb/s) HDTV signals utilizing the developed MLLD and mm-wave PD. Error-free (BER = 10-9, 231 - 1 PRBS, NRZ) outdoor wireless transmission of 3 Gb/s over 25 m is demonstrated, as well as wireless transmission of uncompressed HDTV signals in the 60-GHz band. Finally, an advanced 60-GHz photonic wireless system offering record data throughputs and spectral efficiencies is presented. For the first time, we demonstrate photonic wireless transmission of data throughputs up to 27.04 Gb/s (EVM 17.6%) using a 16-QAM OFDM modulation format resulting in a spectral efficiency as high as 3.86 b/s/Hz. Wireless experiments were carried out within the regulated 57-64-GHz band in a lab environment with a maximum transmit power of - 1 dBm and 23 dBi gain antennas for a wireless span of 2.5 m. This span can be extended to some 100 m when using high-gain antennas and higher transmit power levels.

Hybrid Integrated Optical Phase-Lock Loops for Photonic Terahertz Sources

We present the first hybrid-integrated optical phase-lock loop (OPLL) for use in high spectral purity photonic terahertz sources. We have achieved the necessary short loop delay to lock a 1-MHz linewidth slave laser by hybrid integration of the slave laser and photodetector on a silicon motherboard with silica optical waveguides and combining this with a custom-designed low-delay electronic loop filter circuit. The laser and photodetectors are InP-based and are flip chip bonded to silicon daughter boards, which are in turn attached to the motherboard. Delay between the slave laser and photodiode was approximately 50 ps. The heterodyne between slave and master sources has a linewidth of less than 1 kHz and achieved phase noise less than -80 dBc/Hz at an offset of 10 kHz. The slave laser can be offset from the master source by 2-7 GHz, using a microwave oscillator. This integrated OPLL circuit was used with an optical comb source and an injection-locked laser comb filter to generate high spectral purity signals at frequencies up to 300 GHz with linewidths <;1 kHz and powers of about -20 dBm, while the two integrated lasers could deliver a tunable heterodyne signal at frequencies up to 1.8 THz.

Dynamically controlled channel-to-channel switching in a full-band DS-DBR laser

This paper presents a detailed series of measurements and modeled results that demonstrate rugged switching in a full-band tunable laser between stable, wavelength locked ITU frequencies. During switching a monolithically integrated optical amplifier has been used as a shutter to achieve greater than 40 dB attenuation whilst the wavelength is being tuned. The interactions between the thermal distribution down the laser and the induced frequency deviations are investigated, and the residual frequency deviation of <5 GHz is shown to be predominately thermal.

Monolithically Integrated Photonic Heterodyne System

This paper presents the results from the first monolithically integrated photonic heterodyne system that allows the two optical sources to be mutually phase locked by locking to an external optical reference. High-spectral-purity signals of up to 50 GHz have been demonstrated from this first fabricated device, where the tuning range was limited by losses in the input waveguide. Successful phase locking was accomplished through short signal propagation delay of less than 2 ns achieved by monolithic integration and custom-made fast loop electronics. The approach can be extended to generate signals at >; 1 THz.

Monolithically Integrated Optical Phase Lock Loop for Microwave Photonics

We present a review of the critical design aspects of monolithically integrated optical phase lock loops (OPLLs). OPLL design procedures and OPLL parameters are discussed. A technique to evaluate the gain of the closed loop operating system is introduced and experimentally validated for the first time. A dual-OPLL system, when synchronised to an optical frequency comb generator without any prior filtering of the comb lines, allows generation of high spectral purity signals at any desired frequency from several GHz up to THz range. Heterodyne phase locking was achieved at a continuously tuneable offset frequency between 2 and 6 GHz. Thanks to the photonic integration, small dimensions, and custom-made electronics, the propagation delay in the loop was less than 1.8 ns, allowing good phase noise performance with OPLLs based on lasers with linewidths less than a few MHz. The system demonstrates the potential for photonic integration to be applied in various microwave photonics applications where narrow-bandwidth tuneable optical filters with amplification functionality are required.

Linewidth in Widely Tunable Digital Supermode Distributed Bragg Reflector Lasers: Comparison Between Theory and Measurement

A transfer-matrix-based model is presented for calculating the linewidth of a widely tunable distributed Bragg reflector (DBR) laser as a function of its tuning currents. This model is used to calculate the linewidth of a digital supermode (DS)-DBR laser across its tuning range and compared to linewidth measurements under the same conditions. Excellent agreement is obtained with all the fine structure seen in the measurement being reproduced by the model. This suggests that the dominant factors which determine the complex structure of the linewidth are simple ones such as loss, threshold gain and optical power rather than complex details of the carrier dynamics

Equivalent Performance in C - and L -Bands of Digital Supermode Distributed Bragg Reflector Lasers

New results on the design and performance of digital supermode distributed Bragg reflector lasers for L-band operation are presented. The L-band device, which is fabricated using the same InP-based process as its C-band equivalent is shown to give essentially the same performance. The design changes required are discussed and a detailed comparison presented between C- and L-band devices. Together, a two-chip solution can provide more than 200 consecutive 50-GHz spaced channels (82-nm bandwidth) with SMSR greater than 45 dB and fiber-coupled leveled powers of 13 dBm.

Dynamic control of wavelength switching and shuttering operations in a broadband tunable DS-DBR laser module

Dynamic control of channel switching is demonstrated in a DS-DBR laser module using an integrated optical amplifier as a shutter. Switching time between locked channels is less than 6 ms and frequency deviation less than 5 GHz.

A compact tunable coherent terahertz source based on an hybrid integrated optical phase-lock loop

A tuneable terahertz source based on the first hybrid integrated optical phase-lock loop is presented. Generated signals have linewidth <1kHz and phase noise <−80dBc/Hz at 10kHz offset. The measured output power at 300GHz was −22dBm.