In this paper we explain how to use rate equations to describe a laser that includes integrated optical feedback. We find a relation between the threshold current, the voltage drop at the gain section, output power, linewidth, and side mode suppression ratio, and show experimental results.

Photonic devices and new functions based on HHI's hybrid integration platform PolyBoard are presented providing lowloss thin-film-element-based light routing, an on-chip micro-optical bench and mechanically flexible chips comprising optical and electrical waveguides. The newly developed transfer and integration of graphene layers enables the fabrication of active optoelectronic devices in the intrinsically passive polymer waveguide networks with bandwidths in the GHz range. These novel functionalities in combination with the mature thermo-optic components of the PolyBoard platform such as tunable lasers, switches and variable attenuators pave the way towards new applications of photonic integrated circuits in communications and sensors.

Optical feedback has an impact on the tunability of lasers. We created a model of a tunable distributed Bragg reflector (DBR) laser describing the effect of optical feedback from a constant reflector distance on the wavelength tuning. Theoretical and experimental results are in good agreement. A further discussion of the model sheds light on design rules to reduce the effect of optical feedback on the tuning behavior. We introduced a new parameter called mode loss difference (MLD) as a metric for the feedback tolerance of the tuning behavior. A large MLD indicates higher tolerance of the laser to cavity length variations.

A hybrid polymer/InP dual DBR laser at 1.5μm is presented as an optical source for heterodyne generation and detection of cw-THz signals. The device consists of an active InP chip as an active gain element, end-fire coupled to a polymer chip with thermo-optically tunable phase shifters and Bragg gratings. Mode-hop-free tuning of 1.1 THz has been achieved on the single DBR lasers. The usability of such sources for heterodyne cw-THz generation has been demonstrated in a coherent cw-THz setup. Scans in the THz range show a resolution of the H2O absorption lines comparable to the results achievable with commercially-available external-cavity diode lasers

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We present a model of a tunable distributed Bragg reflector (DBR) laser describing the effect of cavity losses on the gain voltage. Theoretical and experimental results are in good agreement. Measurements show the gain voltage trace for Bragg grating and phase section tuning. The model is also valid for lasers with optical feedback from an external reflection.

This paper presents on-chip free beam optics on polymer-based photonic components. Due to the circumstance that waveguide-based optics allows no direct beam access we use Gradient index (GRIN) lenses assembled into the chip to collimate the beam from the waveguides. This enables low loss power transmission over a length of 1432 µm. Even though the beam propagates through air it is possible to create a resonator with a wavelength shift of 0.002 nm/°C, hence the allowed deviations from the ITU-T grid (100 GHz) are met for ± 20 °C. In order to guarantee reliable laser stability, it is necessary to implement optical isolators at the output of the laser. This requires the insertion of bulk material into the chip and is realized by a 1050 µm thick coated glass. Due to the large gap of the free-space section, it is possible to combine different resonators together. This demonstrates the feasibility of an integrated wavelength-meter.

In this paper we demonstrate the feasibility of low-cost lasers with an integrated wavelength locker and wavelength meter. We use a reflection at the polymer chip to single mode fiber butt coupling point to establish optical feedback outside the laser cavity to make the gain voltage wavelength dependent. With this signal we can keep the alignment of the lasing mode and the Bragg grating optimal and can determine the absolute wavelength of the emitted wavelength without additional hardware.