A quantum cascade laser element includes: a semiconductor substrate; a semiconductor laminate including an active layer having a quantum cascade structure; a first electrode formed on a surface on an opposite side of the semiconductor laminate from the semiconductor substrate; a second electrode; and an insulating film formed on at least one end surface of a first end surface and a second end surface of the semiconductor laminate. The first electrode includes a first metal layer made of a first metal, and a second metal layer made of a second metal having a higher ionization tendency than that of the first metal. The first metal layer has a first region exposed to an outside. The second metal layer has a second region located on one end surface side with respect to the first region. The insulating film reaches the second region from the one end surface.

An optical full-field transmitter for an optical communications network includes a primary laser source configured to provide a narrow spectral linewidth for a primary laser signal, and a first intensity modulator in communication with a first amplitude data source. The first intensity modulator is configured to output a first amplitude-modulated optical signal from the laser signal. The transmitter further includes a first phase modulator in communication with a first phase data source and the first amplitude-modulated optical signal. The first phase modulator is configured to output a first two-stage full-field optical signal. The primary laser source has a structure based on a III-V compound semiconductor.

A tunable laser that includes an array of parallel optical amplifiers is described. The laser may also include an intracavity N×M coupler that couples power between a cavity mirror and the array of parallel optical amplifiers. Phase adjusters in optical paths between the N×M coupler and the optical amplifiers can be used to adjust an amount of power output from M−1 ports of the N×M coupler. A tunable wavelength filter is incorporated in the laser cavity to select a lasing wavelength.

An optical full-field transmitter for an optical communications network includes a primary laser source configured to provide a narrow spectral linewidth for a primary laser signal, and a first intensity modulator in communication with a first amplitude data source. The first intensity modulator is configured to output a first amplitude-modulated optical signal from the laser signal. The transmitter further includes a first phase modulator in communication with a first phase data source and the first amplitude-modulated optical signal. The first phase modulator is configured to output a first two-stage full-field optical signal. The primary laser source has a structure based on a III-V compound semiconductor.

A method (900) includes a gain current (I.sub.GAIN) to an anode of a gain-section diode (D.sub.0) disposed on a shared substrate of a tunable laser (310), delivering a modulation signal to an anode of an Electro-absorption section diode (D.sub.2) disposed on the shared substrate of the tunable laser, and receiving a burst mode signal (330) indicative of a burst-on state or a burst-off state. When the burst mode signal is indicative of the burst-off state, the method includes sinking a sink current (I.sub.SINK) away from the gain current at the anode of the gain-section diode. When the burst mode signal transitions to be indicative of the burst-on state from the burst-off state, the method includes ceasing the sinking of the sink current away from the gain current and delivering an overshoot current (I.sub.OVER) to the anode of the gain-section diode.

A method (900) includes delivering a first bias current (I.sub.GAIN) to an anode of a gain-section diode (590a) and delivering a second bias current (I.sub.PH) to an anode of a phase-section diode (590b). The method also includes receiving a burst mode signal (514) indicative of a burst-on state or a burst-on state, and sinking a first sink current (I.sub.SINK) away from the first bias current when the burst mode signal is indicative of the burst-off state. When the burst mode signal transitions to be indicative of the burst-on state from the burst-off state, the method also includes sinking a second sink current away from the second bias current at the anode of the phase-section diode and ceasing the sinking of the first sink current away from the first bias current at the anode of the gain section diode.

A semiconductor laser comprises a window structure part including a low resistance active layer formed in end face regions, to have a lower resistance than an active layer located inward with respect to the end face regions. A length between the front end of the contact layer and the front end face is longer by 10 μm or more than a length of a front-end-face side window structure part, and is shorter than a length between the front end face and the rear end of the contact layer. A length between an end of a rear side electrode on the side of the front end face and the front end face is 1.2 times or more a substrate thickness of a substrate, and is shorter than a length between the front end face and an end of the rear side electrode on the side of the rear end face.

A thin-film device for a wavelength-tunable semiconductor laser. The device includes a cavity between a high-reflectivity facet and an anti-reflection facet designed to emit a laser light of a wavelength in a tunable range determined by two Vernier-ring resonators with a joint-free-spectral-range between a first wavelength and a second wavelength. The device further includes a film including multiple pairs of a first layer and a second layer sequentially stacking to an outer side of the high-reflectivity facet. Each layer in each pair has one unit of respective optical thickness except one first or second layer in one pair having a larger optical thickness. The film is configured to produce inner reflectivity of the laser light from the high-reflectivity facet at least >90% for wavelengths in the tunable range starting from the first wavelength but at least <50% for wavelengths in a 25 nm range around the second wavelength.

The disclosure describes techniques for forming an ohmic contact layer in a wafer containing CMOS devices and attaching a VCSEL die therein. A composite layer that forms the ohmic contact layer is selected based on the epitaxially-grown compound semiconductor material of the VCSEL die. The ohmic contact layer may not comprise gold, as gold introduces contamination in the rest of the CMOS process. The wafer may have an allocated area for accepting the VCSEL die. The allocated area may have a recess to facilitate placement of the VCSEL die.

What is provided here are: a step of forming a first semiconductor layer on a base member; a step of forming a mask on the first semiconductor layer; a step of etching the first semiconductor layer by using the mask, to thereby form a semiconductor structure; a step of forming a second semiconductor layer in a region abutting on a side surface of the semiconductor structure, said second semiconductor layer having a convex portion abutting to the mask; a convex-portion removing step of removing the convex portion by supplying an etching gas thereto; and a regrown-layer forming step of supplying a material gas onto the semiconductor structure and the second semiconductor layer, to thereby form a regrown layer; wherein the convex-portion removing step and the regrown-layer forming step are executed in a same manufacturing apparatus.