Integrated narrow linewidth laser source with optical amplifier

Abstract

An integrated device for optical power control and stabilization is provided. The integrated device includes a laser source and an optical amplifier operably coupled to the laser source. The laser source emits light having a narrow ray width at an initial output power. An optical amplifier (e.g., a semiconductor optical amplifier) receives and amplifies light from a laser source and emits amplified light. The optical amplifier controls the resulting output power of the emitted amplified light to a configurable level while maintaining a narrow light width in the emitted amplified light and a laser wavelength of the laser source constant. Based on the operation of the reverse bias, the optical amplifier also functions as an optical absorber and suppresses received light having a narrow light ray width without changing the drive current of the laser source.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to and the benefit of provisional patent application "Integrated narrow linewidth laser source with semiconductor optical amplifier for optical power control and stabilization" (Application No. 63 / 589,771) filed with the United States Patent and Trademark Office on October 12, 2023, the entire contents of which are incorporated herein by reference. Technical Field

[0003] Various embodiments of the present disclosure generally relate to optical circuits. More specifically, various embodiments of the present disclosure relate to an integrated narrow linewidth laser source with an optical amplifier for optical power control and stabilization. Background Art

[0004] Various laser applications may require a laser source that emits light having a relatively narrow linewidth (i.e., having a narrow spectrum). These laser sources may be referred to as "narrow linewidth laser sources." These narrow linewidth laser sources may have various applications, including, for example, frequency modulated continuous wave (FMCW) coherent communications, photon sensing, etc. Depending on the operational requirements, it is often necessary to set, control, and stabilize the output power of the light emitted by the narrow linewidth laser source to a specific level depending on environmental conditions.

[0005] Conventional narrow linewidth laser sources may include, for example, distributed feedback lasers and gain chip-based external cavity lasers. The beam width, output power, and laser wavelength of these narrow linewidth laser sources may depend on the drive current of the distributed feedback laser and the gain chip applied to the external cavity laser. Therefore, when the output power of the light emitted by these narrow linewidth laser sources is controlled and stabilized by changing the drive current, the beam width and lasing wavelength will also be affected and changed. Moreover, in the process of controlling and stabilizing the output power of the emitted light, the performance of the narrow linewidth laser source may be affected due to changes in the beam width of the emitted light and changes in the lasing wavelength of the narrow linewidth laser source. Therefore, for various high-precision laser applications, the beam width and lasing wavelength of the narrow linewidth laser source must be kept constant.

[0006] In view of the above situation, a technical solution is needed that can overcome at least one of the above problems. Summary of the invention

[0007] The present application provides an integrated device and method for controlling and stabilizing the output power of a narrow linewidth laser source without any impact on the narrow linewidth and laser wavelength of the narrow linewidth laser source, which is roughly as shown in at least one of the figures and / or described in combination with at least one of the figures, and more fully set forth in the claims.

[0008] These and other features and advantages of the present disclosure may be understood by reading the following detailed description of the disclosure and the accompanying drawings, wherein like reference numerals refer to like parts throughout. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The accompanying drawings illustrate various embodiments of the apparatus, methods and other aspects of the present disclosure by way of example. Therefore, the embodiments herein are not limited to the specific components, structures and methods disclosed herein. In addition, the terms "first", "second" and "third" are used herein only for descriptive purposes and should not be interpreted as indicating or implying relative importance.

[0010] Various embodiments of the present disclosure are illustrated by way of example and not limitation in the figures of the accompanying drawings, in which:

[0011] Figure 1 is a diagram showing an integrated device for optical power control and stabilization according to an embodiment of the present disclosure;

[0012] Figure 2 is a graphical representation showing the spectral distribution of a narrow linewidth laser source and its amplified spectrum according to an embodiment of the present disclosure;

[0013] Figure 3 is a schematic diagram showing an integrated device including a distributed feedback (DFB) laser and a semiconductor optical amplifier (SOA) arranged in a first assembly configuration according to an embodiment of the present disclosure;

[0014] Figure 4 is a diagrammatic view showing an integrated device including a DFB laser and a SOA arranged in a second assembly configuration according to an embodiment of the present disclosure;

[0015] Figure 5A is a diagram showing an integrated device including a DFB laser and a SOA arranged in a third assembly configuration according to an embodiment of the present disclosure;

[0016] Figure 5B and 5C It is shown Figure 5A A diagram of a configuration of a passive tilted waveguide of a DFB laser in an integrated device shown in for spot size conversion;

[0017] Figure 6 is a diagram showing an integrated device including a gain chip-based external cavity laser (ECL) and a SOA arranged in a first assembly configuration according to an embodiment of the present disclosure;

[0018] Figure 7 is a diagram showing an integrated device including a gain chip-based ECL and a SOA arranged in a second assembly configuration according to an embodiment of the present disclosure;

[0019] Figure 8 is a flow chart illustrating a method for controlling the resulting output power of emitted amplified light to a configurable level while maintaining a constant narrow line width in the emitted amplified light according to an embodiment of the present disclosure; and

[0020] Fig. 9 is a flow chart illustrating the operation of an optical amplifier in an integrated device under forward bias and reverse bias according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0021] The present disclosure may be best understood with reference to the detailed drawings and descriptions described herein. Various embodiments are discussed below with reference to the drawings. However, those skilled in the art will readily appreciate that the detailed descriptions provided herein with respect to the drawings are for illustrative purposes only, as the apparatus and methods may extend beyond the described embodiments. In one example, the teachings presented and the needs of a particular application may produce a variety of alternative and suitable methods to implement the functions of any of the details described herein. Therefore, any method may extend beyond the specific implementation selections in the embodiments described and shown below.

[0022] References to "an embodiment," "another embodiment," "yet another embodiment," "one example," "another example," "yet another example," "for example," etc. indicate that the embodiment or example so described may include a particular feature, structure, characteristic, attribute, element, or limitation, but not every embodiment or example must include the particular feature, structure, characteristic, attribute, element, or limitation. Furthermore, repeated use of the phrase "in an embodiment" does not necessarily refer to the same embodiment.

[0023] Various embodiments of the present disclosure may be found in the disclosed apparatus and methods for setting, controlling and stabilizing the output power of light emitted by a narrow linewidth laser source without any impact on the narrow linewidth of the emitted light and the lasing wavelength of the narrow linewidth laser source. Various embodiments of the present disclosure provide an integrated apparatus for controlling the resulting output power of the emitted amplified light to a configurable level while keeping the narrow linewidth and the lasing wavelength in the emitted amplified light constant.

[0024] A narrow linewidth laser source may refer to a laser configured to emit light having a minimum range of optical frequencies or wavelengths, thereby producing a narrow spectral width also referred to as "narrow linewidth". Linewidth may refer to the width of the emission spectrum of a laser source (e.g., full-width at half-maximum "FWHM"), i.e., the width of the range of optical frequencies or wavelengths emitted by the laser source. For a narrow linewidth laser source, the linewidth is quite small, resulting in light being emitted at a very specific and well-defined frequency or wavelength. The narrower the linewidth, the closer the light is to a single frequency with minimal diffusion, resulting in highly monochromatic laser light. In one example, a laser source having a linewidth of less than 1 megahertz (MHz) may be considered to have a narrow linewidth. Therefore, a narrow linewidth laser source may refer to a single-frequency laser source that produces light having a fairly narrow optical emission spectrum or linewidth.

[0025] Narrow linewidths may mean that the light emitted by a narrow linewidth laser source may be highly coherent, with a long coherence length. A longer coherence length allows the light to maintain its phase over a longer distance, which may be useful for applications that rely on stable interference patterns. Therefore, narrower linewidths may enhance the usefulness of narrow linewidth laser sources in applications that require precise wavelength control, high spectral purity, and stability of the emitted light. Narrow linewidth laser sources may be used in a variety of applications, including, for example, frequency-modulated continuous-wave (FMCW) coherent communications, photon sensing, interferometry, and light detection and ranging (LiDAR) systems. The narrow linewidths of the light emitted by these laser sources may provide lower dispersion and higher signal-to-noise ratios (SNR) in these applications.

[0026] The drive current can be used to control the optical output power of a narrow linewidth laser source under its operating temperature conditions. As used herein, "drive current" may refer to a current applied to a laser source to allow the laser source to operate and emit light with a specific output power. The achievable light width of the light emission may depend on the design and construction of the laser chip; however, when the drive current changes, the value of the light width may change. In addition to the light width and output power, the laser wavelength of a narrow linewidth laser source may also depend on the drive current. As used herein, "laser wavelength" may refer to the central wavelength (or frequency) of light that a laser source can emit in its laser mode, and the output spectrum of the laser source is concentrated near this wavelength.

[0027] In view of the above discussion, when the driving current is changed to control and stabilize the output power of the light emitted by the narrow linewidth laser source, the light width and the laser wavelength may also be affected and changed. Typically, the light width may be large under low driving current (e.g., 150 milliamperes (mA)) and low output power conditions, and may be reduced to a smaller value under higher driving current (e.g., 300mA) and high optical power output. Increasing the driving current and output power of the narrow linewidth laser source may affect the light width and laser wavelength of the narrow linewidth laser source. During the control and stabilization of the output power of the narrow linewidth laser source to a specific level according to operating or environmental conditions, the performance of the narrow linewidth laser source must be maintained and must not be affected. Specifically, under the desired operating conditions, the light width should be maintained in its narrow state. In addition, the laser wavelength of the narrow linewidth laser source must be kept constant under the desired operating conditions.

[0028] In order to set, control and stabilize the optical output power of a narrow linewidth laser source without any influence on the light width and laser wavelength, the present disclosure can integrate an optical amplifier (e.g., a semiconductor optical amplifier) ​​with a narrow linewidth laser source. The integration of the optical amplifier can achieve independent control of the optical output power and other performance parameters of the narrow linewidth laser source. By integrating the optical amplifier with the narrow linewidth laser source and operating the integrated optical amplifier, the optical gain of the integrated device can be changed to amplify the output power of the narrow linewidth laser source, and the final optical output of the integrated device can be maintained at a stable optical output power level. As used herein, the term "gain" can refer to a factor that amplifies an input optical signal (e.g., light received from a narrow linewidth laser source). Gain can be measured, for example, as a ratio of output power to input power (in decibels (dB)). The higher the gain, the larger the output optical signal. The integrated device can allow a narrow linewidth laser source to operate at a fixed current to emit light with a narrow linewidth. If operating conditions change and the output power needs to be changed, the integrated device can allow the settings of the narrow linewidth laser source to remain unchanged, while the settings of the optical amplifier can be changed, for example, by changing the drive current applied to the optical amplifier to produce amplified light having the same narrow linewidth and laser wavelength as emitted by the narrow linewidth laser source.

[0029] In various embodiments, the integrated device disclosed herein may include a laser source and an optical amplifier. In one example, the laser source may refer to a distributed feedback laser. In a further example, the laser source may refer to an external cavity laser based on a gain chip. The laser source may be configured to emit light having a narrow light width at an initial output power. The narrow light width may be, for example, in the range of 10 kilohertz (kHz) to 1 MHz. In another example, the narrow light width may be any light width less than 1 MHz. In an embodiment, the optical amplifier may be a semiconductor optical amplifier. The optical amplifier may be operably coupled to the laser source. The optical amplifier may receive light from the laser source, amplify the received light, and emit the amplified light. The optical amplifier may control the resulting output power of the emitted amplified light to a configurable level while keeping the narrow light width in the emitted amplified light constant. In an embodiment, the optical amplifier may keep the laser wavelength of the laser source constant during the period of controlling the resulting output power of the emitted amplified light to a configurable level. The laser wavelength may be, for example, in the O band, C band, or L band of the spectrum. The center wavelength of the O band may be 1310 nanometers (nm), the center wavelength of the C band may be 1550 nm, and the center wavelength of the L band may be 1600 nm. In one embodiment, the optical amplifier in the integrated device may be selected according to the laser wavelength of the laser source. For example, if the laser source is configured to generate a laser wavelength in the O band of the spectrum, an optical amplifier that can operate in the O band is selected to be integrated with the laser source to match the laser source.

[0030] In an embodiment, the laser source may include a laser waveguide extending from a front facet to a rear facet of the laser source. As used herein, a "laser waveguide" may refer to a structure configured to confine and guide light within a specific path within a laser cavity of a laser source to ensure optimal propagation and interaction within the laser source. In various embodiments, the laser waveguide is substantially perpendicular to the front facet and the rear facet of the laser source. The laser waveguide may include a rear end and an output end. In an embodiment, the rear end of the laser waveguide may be configured to be perpendicular to the rear facet of the laser source. In various embodiments, the output end of the laser waveguide may be configured to be perpendicular to the front facet of the laser source. In several embodiments, the output end of the laser waveguide may be configured to be at an angle relative to the front facet of the laser source.

[0031] In various embodiments, the output end of the laser waveguide may be a straight active waveguide. As used herein, a "straight active waveguide" may refer to a linear optical waveguide that can transmit and guide light within a laser source and includes optically active materials or active components that can change the properties of the light or modulate the light. In various embodiments, the output end of the laser waveguide may be a passive tilted waveguide. As used herein, a "passive tilted waveguide" may refer to a type of optical waveguide configured to guide light within a laser source while utilizing tilted interfaces to manage light propagation and coupling. A passive tilted waveguide may not actively amplify or modulate light, but may only guide light. In addition, a passive tilted waveguide may have tilted faces or end faces that affect how light is coupled into and out of the waveguide or interacts with other optical components. In further embodiments, a passive tilted waveguide may be configured as a spot size converter that is aligned with an optical mode of an optical amplifier.

[0032] In an embodiment, an optical amplifier may include an amplifier waveguide extending from an input face of the optical amplifier to an output face. As used herein, an "amplifier waveguide" may refer to a structure configured to confine and guide light received from a narrow linewidth laser source into a specific path in the optical amplifier to ensure optimal propagation and interaction within the optical amplifier. In various embodiments, the amplifier waveguide may be substantially perpendicular to the input face and output face of the optical amplifier. The amplifier waveguide may include an input end and an output end. The input end of the amplifier waveguide may refer to an input waveguide portion of the amplifier waveguide. The output end of the amplifier waveguide may refer to an output waveguide portion of the amplifier waveguide. In an embodiment, the input end of the amplifier waveguide may be configured to be perpendicular to the input face of the optical amplifier. In other embodiments, the input end of the amplifier waveguide may be configured to be angled relative to the input face of the optical amplifier. In various embodiments, the input end of the amplifier waveguide may be a straight waveguide. In various embodiments, the input end of the amplifier waveguide may be an optically transparent angled waveguide. In various embodiments, the output end of the amplifier waveguide may be configured to be at an angle relative to the output face of the optical amplifier. In additional embodiments, the integrated device may include an anti-reflection coating on an input end at an input facet of the optical amplifier and an output end at an output facet of the optical amplifier.The output end of the laser waveguide may be optically coupled to the input end of the amplifier waveguide.

[0033] In various embodiments, the optical amplifier can be oriented relative to the laser source so that the optical axis of the laser source is aligned with the input optical axis of the optical amplifier. The input optical axis of the optical amplifier can refer to the optical axis of the input end (or input waveguide portion) of the amplifier waveguide. In an embodiment, the optical axis of the laser source can be colinear with the input optical axis of the optical amplifier.

[0034] In an embodiment, the integrated device may further include at least one controller operably coupled to the laser source. The controller may be configured to control the applied drive current that maintains the initial output power of the light. In another embodiment, the integrated device may further include at least one controller operably coupled to the optical amplifier. The controller may be configured to change the optical gain of the optical amplifier to amplify the initial output power of the light from the laser source and stabilize the resulting output power to a configurable level. In several embodiments, the optical amplifier may be further configured to adjust the optical power drift of the initial output power of the light from the laser source during the control of the resulting output power of the emitted amplified light to a configurable level.

[0035] In an embodiment, an optical amplifier of an integrated device may be configured to operate in reverse bias and forward bias. In various embodiments, in response to operation in forward bias, the optical amplifier may receive light from a laser source, amplify the received light, emit the amplified light, and control the resulting output power of the emitted amplified light to a configurable level while maintaining a narrow line width in the emitted amplified light constant. In various embodiments, in response to operation in reverse bias, the optical amplifier may operate as a light absorber and suppress received light having a narrow line width without changing the drive current of the laser source.

[0036] Reference now Figure 1 , a block diagram 100 of an integrated device 102 for optical power control and stabilization according to an embodiment of the present disclosure is shown. The integrated device 102 disclosed herein may include a narrow linewidth laser source 104 configured to emit light 108 having a narrow line width at an initial output power. In an example, the narrow linewidth laser source 104 may be a distributed feedback (DFB) laser operating in the infrared wavelength region of the electromagnetic spectrum. A DFB laser may refer to a laser device whose active medium may include a repeating corrugated structure. The corrugated structure may be a periodic variation of a refractive index, thereby acting as a diffraction grating that provides optical feedback throughout the corrugated structure. Therefore, the DFB laser may emit only a single wavelength, thereby being able to produce a fairly narrow line width output. The DFB laser may emit light 108 having a narrow line width of, for example, 1 kilohertz (kHz) to 1 megahertz (MHz), and an output power of tens of milliwatts (mW) or more than 100 mW. In another example, the narrow linewidth laser source 104 may be an external cavity laser (ECL) based on a gain chip. Gain chip based ECLs can operate over a range of wavelengths based on the gain medium and the design of the ECL.The light 108 emitted by narrow linewidth laser source 104 can be, for example, continuous wave, pulsed light, or light modulated in any manner suitable for a given application.

[0037] The integrated device 102 may also include an optical amplifier 106 . Figure 1The integration of the narrow linewidth laser source 104 and the optical amplifier 106 is shown. In an embodiment, the optical amplifier 106 may be a semiconductor optical amplifier (SOA). An SOA may refer to a device that amplifies light by stimulated emission of radiation using a semiconductor material as a gain medium. For the purpose of illustration, the disclosure herein refers to the optical amplifier 106 being an SOA; however, the scope of the disclosure herein is not limited to the optical amplifier 106 being an SOA, but extends to include any optical amplifier configured to set, control, and stabilize the output power of the light 110 emitted by the integrated device 102 without any effect on the narrow linewidth of the emitted light 108 and the laser wavelength of the narrow linewidth laser source 104.

[0038] An optical amplifier 106 (interchangeably referred to as "SOA 106") is operably coupled to a narrow linewidth laser source 104. In an embodiment, an output port of the narrow linewidth laser source 104 may be operably coupled to an input port of the SOA 106 to allow the SOA 106 to receive light 108 having a narrow linewidth from the output port of the narrow linewidth laser source 104 at an initial output power. In various embodiments, to couple the narrow linewidth laser source 104 to the SOA 106, the mode field diameters of the narrow linewidth laser source 104 and the SOA 106 may be aligned to minimize losses. Such alignment may require that the optical modes of the laser output and the SOA input are compatible, which may require a lens or an optical fiber to properly couple the light 108. In various embodiments, the output port of the narrow linewidth laser source 104 may be coupled to the input port of the SOA 106 via an optical fiber, for example, using a fiber-to-fiber coupling technique, a fiber-to-endface coupling technique, etc. The SOA 106 can operate at signal wavelengths between, for example, 850 nanometers (nm) and 1600 nm, and can generate up to 30 decibels (dB) of gain. In one embodiment, the gain profile of the SOA 106 can be wider than the narrow linewidth of the light 108 emitted by the narrow linewidth laser source 104. In various embodiments, the gain of the SOA 106 can be configured to be constant over the operating wavelength range, thereby allowing uniform amplification of the received light 108 regardless of wavelength and keeping the narrow linewidth of the amplified light 110 constant.

[0039] The SOA 106 can receive light 108 from the narrow linewidth laser source 104 and amplify the received light 108. The received light 108 can pass through a narrow path in the semiconductor material of the SOA 106. When the SOA 106 receives the light 108 from the narrow linewidth laser source 104, the received light 108 can interact with excited electrons in an active gain layer, which includes a bulk layer, quantum well, quantum wire, or quantum dot of a semiconductor material. Through the process of stimulated emission, these electrons lose energy and emit photons of the same wavelength as the received light 108, thereby generating a population inversion, thereby generating gain in the semiconductor material. When the received light 108 passes through the SOA 106, the gain amplifies the received light 108. Therefore, amplified light 110 is emitted from the SOA 106 and maintains the wavelength of the received light 108. In SOA 106, electric carriers can be injected by driving current to increase the optical power of received light 108 while maintaining basic physical properties of received light 108, such as polarization, narrow beam width, and frequency. As the driving current increases, the optical output power also increases based on a certain function.

[0040] After amplification, the SOA 106 may emit amplified light 110 through an output port of the SOA 106. The SOA 106 may control the resulting output power of the emitted amplified light 110 to a configurable level while maintaining a narrow line width in the emitted amplified light 110 constant. In an embodiment, the SOA 106 may maintain a laser wavelength of the narrow line width laser source 104 constant during the control of the resulting output power of the emitted amplified light 110 to a configurable level. That is, the emitted amplified light 110 may have the same narrow line width and laser wavelength as the light 108 emitted by the narrow line width laser source 104. In various embodiments, the narrow line width laser source 104 may be driven to operate at temperature and current settings to meet performance parameters of narrow line width and laser wavelength. In order to achieve the narrow line width in the narrow line width laser source 104, several design considerations are implemented, such as active waveguide design and device length. For example, a longer narrow line width laser source 104 may emit light 108 with a narrower line width. The target narrow line width may be achieved at a specific operating current of the narrow line width laser source 104. Any fine tuning of the resulting output power of the emitted amplified light 110 can be achieved by driving the SOA 106 to achieve the optical gain required for the desired output power under continuous monitoring. The resulting output power of the integrated device 102 can be fine tuned by changing the drive current of the SOA 106, which in turn can change the optical gain of the SOA 106. In this way, the narrow line width and laser wavelength can remain unchanged, while the optical output power can be varied as required. In further embodiments, the SOA 106 can also be used to balance any optical power drift or variation from the narrow line width laser source 104 to achieve a stable optical output. By changing the drive current of the SOA 106 to adjust its optical gain, any power drift from the narrow line width laser source 104 can be compensated and any power variation can be balanced.

[0041] In an embodiment, the integrated device 102 may further include at least one controller 112 operably coupled to the narrow linewidth laser source 104. The controller 112 may be configured to control the applied drive current to maintain the initial output power of the light 108. In various embodiments, the controller 112 may compare the measured output power with a predefined set point (i.e., the desired output power) using a feedback loop. The difference between the actual output power and the desired output power may be used to adjust the drive current that may be applied to the narrow linewidth laser source 104. In various embodiments, the integrated device 102 may further include at least one controller 114 operably coupled to the SOA 106. The controller 114 may be configured to change the optical gain of the SOA 106 to amplify the initial output power of the light 108 from the narrow linewidth laser source 104, and stabilize the resulting output power of the emitted amplified light 110 to a configurable level.

[0042] The output power of the narrow linewidth laser source 104 is controlled by its operating current and the laser chip temperature. Then, the SOA 106 can be operated so that its gain spectrum can overlap with the emission spectrum of the narrow linewidth laser source 104, and the drive current of the SOA 106 can be set to achieve the optical gain required to obtain the resulting output power of the integrated device 102. In further embodiments, the SOA 106 can be configured to adjust the optical power drift of the initial output power of the light 108 from the narrow linewidth laser source 104 during the control of the resulting output power of the emitted amplified light 110 to a configurable level. In several embodiments, the integrated device 102 including the narrow linewidth laser source 104 and the SOA 106 can be manufactured by conventional manufacturing processes of epitaxial layer growth, waveguide formation, contact metallization, strip cutting, optical coating deposition, and final chip cutting. In various embodiments, the integrated device 102 including the narrow linewidth laser source 104 and the SOA 106 can be mounted on any heat dissipating substrate, such as made of aluminum nitride, silicon carbide, etc.

[0043] For brevity, the ongoing description is directed to SOA 106 integrated with a DFB laser or a gain chip based ECL. However, in various embodiments, integrated device 102 may operate in a similar manner with other optical amplifiers integrated with other types of narrow linewidth laser sources to perform similar or different functions.

[0044] Figure 2 FIG. 2 is a graph 200 showing the spectrum distribution of the narrow linewidth laser source 104 and its amplified spectrum according to an embodiment of the present invention. Figure 1 Describing graph 200. Spectral distribution may be represented by wavelength on the horizontal axis and output power on the vertical axis. Figure 2 The graph 200 in FIG. 2 shows a spectral profile 202 of a narrow linewidth laser source 104 (eg, a DFB laser) where the optical power density Po(λ) increases to its peak value (referred to as the lasing wavelength) and then decreases to a power baseline. Figure 2 The graph 200 in FIG. 1 also shows an output spectral profile 204 of the SOA 106, showing the amplification of the light 108 received from the narrow linewidth laser source 104. The line width Δλ may refer to the wavelength interval between two points where the optical power density is half of its peak power density value, such as Figure 2 206 and 208 in FIG. After the emitted light 108 received from the narrow linewidth laser source 104 propagates through the SOA 106, the optical power can be increased to GPo(λ), where G is the optical gain or amplification factor. The SOA 106 can control the resulting output power of the emitted amplified light 110 to a configurable level while maintaining a constant narrow linewidth Δλ in the emitted amplified light 110. Figure 2As shown, although the resulting output power of the emitted amplified light 110 is higher than the initial output power of the light 108 received from the narrow linewidth laser source 104, the narrow line width of the emitted amplified light 110 remains unchanged. That is, the integrated device 102 disclosed herein maintains the narrow line width of the light 108 emitted from the narrow linewidth laser source 104 and the narrow line width in the amplified light 110 emitted from the SOA 106 constant.

[0045] Figure 3 is a block diagram illustrating an integrated device 300 according to an embodiment of the present disclosure, the integrated device 300 including a distributed feedback (DFB) laser 302 and an SOA 304 arranged in a first assembly configuration. The DFB laser 302 may be used as a narrow linewidth laser source configured to emit light 314 having a narrow linewidth at an initial output power. The DFB laser 302 may include a rear facet 302A, a front facet 302B, and a laser waveguide 306 extending from the rear facet 302A to the front facet 302B. In an embodiment, the laser waveguide 306 is substantially perpendicular to the rear facet 302A and the front facet 302B of the DFB laser 302. The laser waveguide 306 may include a rear end 306A and an output end 306B. In an embodiment, the rear end 306A of the laser waveguide 306 may be perpendicular to the rear facet 302A of the DFB laser 302, as Figure 3 In another embodiment, the output end 306B of the laser waveguide 306 may be perpendicular to the front end face 302B of the DFB laser 302, as shown in FIG. Figure 3 In various embodiments, the output end 306B of the laser waveguide 306 may be a straight active waveguide.

[0046] In addition, SOA 304 may include an input facet 304A, an output facet 304B, and an amplifier waveguide 308 extending from the input facet 304A to the output facet 304B. In one embodiment, the amplifier waveguide 308 is substantially perpendicular to the input facet 304A and the output facet 304B of SOA 304. The amplifier waveguide 308 may include an input end 308A and an output end 308B. The input end 308A of the amplifier waveguide 308 may refer to an input waveguide portion of the amplifier waveguide 308. The output end 308B of the amplifier waveguide 308 may refer to an output waveguide portion of the amplifier waveguide 308. In various embodiments, the input end 308A of the amplifier waveguide 308 may be tilted (angled) relative to the input facet 304A of the SOA 304, such as Figure 3 In such an embodiment, the input end 308A of the amplifier waveguide 308 may be an optically transparent tilted waveguide. In another embodiment, the output end 308B of the amplifier waveguide 308 may be at an angle relative to the output face 304B of the SOA 304, such as Figure 3Thus, in a first assembly configuration, the laser waveguide 306 of the DFB laser 302 may be straight and perpendicular to the rear facet 302A and the front facet 302B, while the SOA 304 may include a waveguide that is angled at two of its faces, namely the input facet 304A and the output facet 304B.

[0047] In a first assembly configuration, the output end 306B of the straight laser waveguide 306 of the DFB laser 302 can be optically coupled into the angled input end 308A of the amplifier waveguide 308 of the SOA 304. In one embodiment, the two chips, namely the DFB laser 302 and the SOA 304, can be closely butt-coupled to each other. In another embodiment, the DFB laser 302 and the SOA 304 can be closely lens-coupled to each other. In one example, the output end 306B of the laser waveguide 306 of the DFB laser 302 can be optically coupled into the input end 308A of the amplifier waveguide 308 of the SOA 304 using a microlens. In such an embodiment, the output end 306B of the laser waveguide 306 of the DFB laser 302 can be optically coupled into the input end 308A of the amplifier waveguide 308 of the SOA 304 using a microlens. Figure 3 In various embodiments shown, the SOA 304 can be oriented relative to the DFB laser 302 such that the optical axis 310 of the DFB laser 302 can be aligned with the input optical axis 312 of the SOA 304. The input optical axis 312 of the SOA 304 can refer to the optical axis of the input end 308A (or input waveguide portion) of the amplifier waveguide 308. In such embodiments, the optical axis 310 of the DFB laser 302 can be co-linear with the input optical axis 312 of the SOA 304. For example, since the input end 308A of the amplifier waveguide 308 is angled, the SOA 304 can be tilted such that the input optical axis 312 of the SOA 304 matches the optical axis 310 of the DFB laser 302. In various embodiments, the angle of the input end 308A of the amplifier waveguide 308 can be configured to be very small, so that the tilt angle between the DFB laser 302 and the SOA 304 can also be very small to achieve low-loss optical coupling. Low-loss optical coupling may refer to techniques and methods for coupling the DFB laser 302 to the SOA 304 with minimal optical power loss, thereby allowing efficient transmission of the light 314 from the DFB laser 302 to the SOA 304, thereby ensuring that a majority of the light 314 is preserved during the coupling process. In one embodiment, one of the design considerations for achieving low-loss optical coupling may be matching the exit direction of the DFB laser 302 output with the optical input direction of the SOA 304.

[0048] In various embodiments, the DFB laser 302 may include a laser gain medium layer and a guide layer, which are sandwiched between a p-type and an n-type semiconductor. The guide layer may include a corrugated structure responsible for providing distributed optical feedback. The p-type layer and the n-type layer may have metal deposition on their outer surfaces to enable current input, which provides pump energy and thus supports the laser action in the DFB laser 302. The DFB laser 302 may emit light 314 with a narrow line width at an initial output power. The SOA 304 may receive the light 314 emitted by the DFB laser 302 at an input face 304A, amplify the received light 314 as the received light 314 propagates from the input face 304A to the output face 304B along an amplifier waveguide 308 of the SOA 304, and emit amplified light 316 from the output face 304B. The SOA 304 may control the resulting output power of the emitted amplified light 316 to a configurable level while keeping the narrow line width in the emitted amplified light 316 constant. SOA 304 can also maintain the lasing wavelength of DFB laser 302 constant while controlling the resulting output power of emitted amplified light 316 to a configurable level. That is, emitted amplified light 316 can have the same narrow line width and lasing wavelength as light 314 emitted by DFB laser 302.

[0049] Figure 4 is a block diagram illustrating an integrated device 400 according to an embodiment of the present disclosure, the integrated device including a DFB laser 402 and an SOA 404 arranged in a second assembly configuration. The DFB laser 402 can be used as a narrow linewidth laser source, which is configured to emit light 414 with a narrow linewidth at an initial output power. The DFB laser 402 may include a rear facet 402A, a front facet 402B, and a laser waveguide 406 extending from the rear facet 402A to the front facet 402B. In an embodiment, the laser waveguide 406 is substantially perpendicular to the rear facet 402A and the front facet 402B of the DFB laser 402. The laser waveguide 406 may include a rear end 406A and an output end 406B. In an embodiment, the rear end 406A of the laser waveguide 406 may be perpendicular to the rear facet 402A of the DFB laser 402, as Figure 4 In another embodiment, the output end 406B of the laser waveguide 406 may be perpendicular to the front end face 402B of the DFB laser 402, as shown in FIG. Figure 4 In various embodiments, the output end 406B of the laser waveguide 406 may be a straight active waveguide.

[0050] In addition, SOA 404 may include an input face 404A, an output face 404B, and an amplifier waveguide 408 extending from the input face 404A to the output face 404B. In one embodiment, the amplifier waveguide 408 is substantially perpendicular to the input face 404A and the output face 404B of SOA 404. The amplifier waveguide 408 may include an input end 408A and an output end 408B. The input end 408A of the amplifier waveguide 408 may refer to an input waveguide portion of the amplifier waveguide 408. The output end 408B of the amplifier waveguide 408 may refer to an output waveguide portion of the amplifier waveguide 408. In various embodiments, the input end 408A of the amplifier waveguide 408 may be perpendicular to the input face 404A of the SOA 404, such as Figure 4 In such an embodiment, the input end 408A of the amplifier waveguide 408 may be a straight waveguide. In another embodiment, the output end 408B of the amplifier waveguide 408 may be at an angle relative to the output face 404B of the SOA 404, such as Figure 4 Thus, in the second assembly configuration, the laser waveguide 406 of the DFB laser 402 may be straight and perpendicular to the rear facet 402A and the front facet 402B, while the SOA 404 may include a straight waveguide at its input facet 404A and an angled waveguide at its output facet 404B.

[0051] In a second assembly configuration, the output end 406B of the straight laser waveguide 406 of the DFB laser 402 can be optically coupled to the straight input end 408A of the amplifier waveguide 408 of the SOA 404. In one embodiment, the two chips, namely the DFB laser 402 and the SOA 404, can be closely coupled to each other. In another embodiment, the DFB laser 402 and the SOA 404 can be closely lens coupled to each other. In one example, the output end 406B of the laser waveguide 406 of the DFB laser 402 can be optically coupled to the input end 408A of the amplifier waveguide 408 of the SOA 404 using a microlens. In such an embodiment, the output end 406B of the laser waveguide 406 of the DFB laser 402 can be optically coupled to the input end 408A of the amplifier waveguide 408 of the SOA 404 using a microlens. Figure 4 In the various embodiments shown, the SOA 404 can be oriented relative to the DFB laser 402 such that the optical axis 410 of the DFB laser 402 can be aligned with the input optical axis 412 of the SOA 404. The input optical axis 412 of the SOA 404 can refer to the optical axis of the input end 408A (or input waveguide portion) of the amplifier waveguide 408. In such an embodiment, the optical axis 410 of the DFB laser 402 can be co-linear with the input optical axis 412 of the SOA 404. In a second assembly configuration, the input end 408A of the amplifier waveguide 408 of the SOA 404 can be modified to be straight to allow the input end 408A to receive the incident light 414 from the DFB laser 402 without any tilting of the SOA 404.

[0052] In an embodiment, for all configurations of the SOA 404, an anti-reflection coating (not shown) is applied to the input end 408A at the input face 404A and the output end 408B at the output face 404B of the SOA 404. Since the input end 408A of the amplifier waveguide 408 of the SOA 404 may be straight and perpendicular to the input face 404A of the SOA 404, the anti-reflection coating applied to the straight input face 404A must have a relatively low reflectivity, for example, much less than 10 -4 , to substantially suppress any back reflections from the input face 404A. Figure 4 In the second assembly configuration shown in FIG. 4 , the anti-reflection coating on the straight input face 404A of the SOA 404 can be enhanced to have a relatively low reflectivity to minimize back reflections from the straight input face 404A without affecting the performance of the SOA 404. In addition, in one embodiment, one of the design considerations for achieving low-loss optical coupling between the DFB laser 402 and the SOA 404 can be to ensure a minimum spacing between the chips of the DFB laser 402 and the SOA 404 when the front face 402B of the DFB laser 402 and the input face 404A of the SOA 404 are parallel to each other, such as Figure 4 shown.

[0053] In various embodiments, the DFB laser 402 may include a laser gain medium layer and a guide layer, such as Figure 3 As shown. The DFB laser 402 may emit light 414 having a narrow line width at an initial output power. The SOA 404 may receive the light 414 emitted by the DFB laser 402 at an input face 404A, amplify the received light 414 as it propagates from the input face 404A to the output face 404B along an amplifier waveguide 408 of the SOA 404, and emit amplified light 416 from the output face 404B. The SOA 404 may control the resulting output power of the emitted amplified light 416 to a configurable level while keeping the narrow line width in the emitted amplified light 416 constant. The SOA 404 may also keep the laser wavelength of the DFB laser 402 constant while controlling the resulting output power of the emitted amplified light 416 to a configurable level. That is, the emitted amplified light 416 may have the same narrow line width and laser wavelength as the light 414 emitted by the DFB laser 402.

[0054] Figure 5A5 is a block diagram illustrating an integrated device 500 according to an embodiment of the present disclosure, the integrated device 500 including a DFB laser 502 and an SOA 504 arranged in a third assembly configuration. The DFB laser 502 may be used as a narrow linewidth laser source configured to emit light 514 having a narrow linewidth at an initial output power. The DFB laser 502 may include a rear facet 502A, a front facet 502B, and a laser waveguide 506 extending from the rear facet 502A to the front facet 502B. In one embodiment, the laser waveguide 506 is substantially perpendicular to the rear facet 502A and the front facet 502B of the DFB laser 502. The laser waveguide 506 may include a rear end 506A and an output end 506B. The rear end 506A of the laser waveguide 506 may refer to a rear waveguide portion of the laser waveguide 506. The output end 506B of the laser waveguide 506 may refer to an output waveguide portion of the laser waveguide 506. In one embodiment, the rear end 506A of the laser waveguide 506 may be perpendicular to the rear end face 502A of the DFB laser 502. Figure 5A In another embodiment, the output end 506B of the laser waveguide 506 may be at a certain angle relative to the front face 502B of the DFB laser 502, such as Figure 5A shown.

[0055] In various embodiments, the output end 506B of the laser waveguide 506 may be a passive tilted waveguide. In other words, the DFB laser 502 may be configured with a passive tilted waveguide that matches the tilted input of the SOA 504. In one embodiment, the passive tilted waveguide of the DFB laser 502 may be configured as a spot size converter to better match the optical mode of the SOA 504. As a spot size converter, the passive tilted waveguide may be configured to adjust the size of the output beam of light 514 emitted by the DFB laser 502 to align with the optical mode of the SOA 504. In this embodiment, since the passive tilted waveguide of the DFB laser 502 matches the tilted input of the SOA 504, the SOA 504 does not have to be tilted. Therefore, the two chips, namely the DFB laser 502 and the SOA 504, may be arranged very close to each other, thereby minimizing the coupling loss between the two chips. In one embodiment, one of the design considerations for achieving low-loss optical coupling between the DFB laser 502 and the SOA 504 may be to ensure a minimum spacing between the chips of the DFB laser 502 and the SOA 504 when the front facet 502B of the DFB laser 502 and the input facet 504A of the SOA 504 are parallel to each other, such as Figure 5A In addition to minimizing the tilt requirement between the DFB laser 502 and the SOA 504, in one embodiment, a refractive index matching gel may be inserted in the gap between the two chips to further reduce reflections and improve optical coupling between the two chips.

[0056] In addition, SOA 504 may include an input face 504A, an output face 504B, and an amplifier waveguide 508 extending from the input face 504A to the output face 504B. In one embodiment, the amplifier waveguide 508 is substantially perpendicular to the input face 504A and the output face 504B of the SOA 504. The amplifier waveguide 508 may include an input end 508A and an output end 508B. The input end 508A of the amplifier waveguide 508 may refer to an input waveguide portion of the amplifier waveguide 508. The output end 508B of the amplifier waveguide 508 may refer to an output waveguide portion of the amplifier waveguide 508. In various embodiments, the input end 508A of the amplifier waveguide 508 may be angled relative to the input face 504A of the SOA 504, such as Figure 5A In such an embodiment, the input end 508A of the amplifier waveguide 508 may be an angled waveguide. In another embodiment, the output end 508B of the amplifier waveguide 508 may be at an angle relative to the output face 504B of the SOA 504, such as Figure 5A Thus, in the third assembly configuration, the laser waveguide 506 of the DFB laser 502 may be straight and vertical at the rear face 502A and angled at the front face 502B, while the SOA 504 may include angled waveguides at both faces thereof, namely the input face 504A and the output face 504B.

[0057] In such Figure 5A In the various embodiments shown, the SOA 504 can be oriented relative to the DFB laser 502 such that the output optical axis 510 of the DFB laser 502 can be aligned with the input optical axis 512 of the SOA 504. The output optical axis 510 of the DFB laser 502 can refer to the optical axis of the output end 506B (or output waveguide portion) of the laser waveguide 506. The input optical axis 512 of the SOA 504 can refer to the optical axis of the input end 508A (or input waveguide portion) of the amplifier waveguide 508. In such embodiments, the output optical axis 510 of the DFB laser 502 can be co-linear with the input optical axis 512 of the SOA 504. In a third assembly configuration, the angled output end 506B of the laser waveguide 506 of the DFB laser 502 can be optically coupled into the angled input end 508A of the amplifier waveguide 508 of the SOA 504. Furthermore, as a spot size converter, the passive tilted waveguide at the output end 506B of the laser waveguide 506 may allow optical coupling of light 514 between the output end 506B of the laser waveguide 506 and the input end 508A of the amplifier waveguide 508 .

[0058] In various embodiments, the DFB laser 502 may include a Figure 3The DFB laser 502 may emit light 514 having a narrow line width at an initial output power. The SOA 504 may receive the light 514 emitted by the DFB laser 502 at an input facet 504A, amplify the received light 514 as it propagates from the input facet 504A to the output facet 504B along the amplifier waveguide 508 of the SOA 504, and emit amplified light 516 from the output facet 504B. The SOA 504 may control the resulting output power of the emitted amplified light 516 to a configurable level while keeping the narrow line width in the emitted amplified light 516 constant. During the control of the resulting output power of the emitted amplified light 516 to a configurable level, the SOA 504 may also keep the laser wavelength of the DFB laser 502 constant. That is, the emitted amplified light 516 may have the same narrow line width and laser wavelength as the light 514 emitted by the DFB laser 502.

[0059] Figure 5B and 5C It is shown Figure 5A Schematic diagrams of configurations 518A and 518B of passive tilted waveguides of a DFB laser 502 in an integrated device 500 shown in FIG. 5 for spot size conversion. The passive tilted waveguide of the DFB laser 502 may be formed at the emission end, i.e., the output end 506B of the laser waveguide 506 of the DFB laser 502. In an embodiment, the output end 506B of the laser waveguide 506 may be configured as follows: Figure 5B The tapered waveguide structure shown is used for spot size conversion. The tapered extended waveguide structure can gradually transition from a smaller cross-sectional area to a larger cross-sectional area at the output end 506B of the laser waveguide 506. This gradual expansion can help minimize reflections and signal losses that may occur during the waveguide size change. The output end 506B of the laser waveguide 506 can be gradually tapered at the front face 502B of the DFB laser 502, such as Figure 5B In various embodiments, the output end 506B of the laser waveguide 506 may be configured as follows: Figure 5C The tapered waveguide structure shown is used for spot size conversion. The tapered waveguide structure can gradually transition from a larger cross-sectional area to a smaller cross-sectional area at the output end 506B of the laser waveguide 506. This gradual transition can help minimize reflections and signal losses that may occur during the waveguide size change. The output end 506B of the laser waveguide 506 can gradually taper to the front face 502B of the DFB laser 502, such as Figure 5C The tapered expansion waveguide structure and the tapered contraction waveguide structure may be configured to match their far-field divergence with the far-field divergence of the input end 508A of the amplifier waveguide 508 of the SOA 504 .

[0060] Figure 6is a schematic diagram showing an integrated device 600 according to an embodiment of the present disclosure, which includes a gain chip-based external cavity laser (ECL) 602 and an SOA 610 arranged in a first assembly configuration. The gain chip-based ECL 602 can refer to a laser in which the gain medium is a separate, typically discrete gain chip 606, which is used in conjunction with an external optical cavity to produce a stable and tunable laser output. The gain chip 606 can refer to a semiconductor device that provides the optical gain required to amplify the light. In an embodiment, the gain chip 606 may include a diode laser or a similar structure that can be electrically pumped to produce coherent light. The gain chip 606 can generate an initial optical signal that can subsequently be amplified within an external optical cavity. The external optical cavity surrounding the gain chip 606 can be used to provide feedback and control the output characteristics of the gain chip-based ECL 602. The external optical cavity may include one or more reflectors, lenses, or diffraction gratings. In an embodiment, the gain chip 606 can include a diode laser or a similar structure that can be electrically pumped to produce coherent light. The gain chip 606 can generate an initial optical signal that can subsequently be amplified within an external optical cavity. The external optical cavity surrounding the gain chip 606 can be used to provide feedback and control the output characteristics of the gain chip-based ECL 602. The external optical cavity may include one or more reflectors, lenses, or diffraction gratings. Figure 6 In the illustrated embodiment, the gain chip based ECL 602 may include a reflector 604 in an external optical cavity, such as a mirror, another silicon photonic chip, a fiber Bragg grating, etc. The external optical cavity may define the emission wavelength of the gain chip based ECL 602 and help stabilize and narrow the optical width of the laser output. The external optical cavity may also provide feedback to the gain chip 606 and may be adjusted to tune the laser output.

[0061] The gain chip based ECL 602 may be used as a narrow line width laser source configured to emit light 616 having a narrow line width at an initial output power. The gain chip 606 of the gain chip based ECL 602 may include a rear facet 606A, a front facet 606B, and a laser waveguide 608 extending from the rear facet 606A to the front facet 606B. In an embodiment, the laser waveguide 608 is substantially perpendicular to the rear facet 606A and the front facet 606B of the gain chip 606. The laser waveguide 608 may include a rear end 608A and an output end 608B. In an embodiment, the rear end 608A of the laser waveguide 608 may be at an angle relative to the rear facet 606A of the gain chip 606, such as Figure 6 In such an embodiment, the rear end 608A of the laser waveguide 608 may be an inclined waveguide. In a further embodiment, the output end 608B of the laser waveguide 608 may be perpendicular to the front end face 606B of the gain chip 606, as shown in FIG. Figure 6 In such an embodiment, the output end 608B of the laser waveguide 608 may be a straight active waveguide.

[0062] The gain chip 606 of the gain chip based ECL 602 can be integrated with the SOA 610, such as Figure 6As shown. In an embodiment, the gain chip 606 may have a surface reflectivity based on anti-reflection on the inclined rear end facet 606A and low reflection on the normal front end facet 606B. The laser waveguide 608 of the gain chip 606 may include an inclined rear end 608A extending to the rear end facet 606A, which is coated with an anti-reflection coating; and a normal output end 608B extending to the front end facet 606B, which is coated with a low-reflection coating. The gain chip-based ECL 602 is formed between: (a) a reflector 604, which is coupled to the inclined rear end 608A of the laser waveguide 608 at the rear end facet 606A coated with an anti-reflection coating; and (b) a normal output end 608B of the laser waveguide 608 at the front end facet 606B coated with a low-reflection coating. The reflectivity of the anti-reflection rear end facet 606A may be less than 10 -4 , and the reflectivity of the low-reflection front facet 606B can be in the range of several % to several tens of %, depending on the design of the gain chip-based ECL 602. The reflectivity of the reflector 604 and the anti-reflection and low-reflection surface reflectivities of the gain chip 606 can determine the optical output power of the gain chip-based ECL 602. In another embodiment, the gain chip-based ECL 602 is formed by coupling the light output 614 from the anti-reflection tilted rear facet 606A of the gain chip 606 to the reflector 604. Then, the light 616 can be emitted from the low-reflection normal front facet 606B of the gain chip 606 to be coupled into the SOA 610.

[0063] In addition, the SOA 610 may include an input face 610A, an output face 610B, and an amplifier waveguide 612 extending from the input face 610A to the output face 610B. In an embodiment, the amplifier waveguide 612 is substantially perpendicular to the input face 610A and the output face 610B of the SOA 610. The amplifier waveguide 612 may include an input end 612A and an output end 612B. The input end 612A of the amplifier waveguide 612 may refer to an input waveguide portion of the amplifier waveguide 612. The output end 612B of the amplifier waveguide 612 may refer to an output waveguide portion of the amplifier waveguide 612. In various embodiments, the input end 612A of the amplifier waveguide 612 may be angled relative to the input face 610A of the SOA 610, such as Figure 6 In another embodiment, the output end 612B of the amplifier waveguide 612 may be angled relative to the output face 610B of the SOA 610, as shown in FIG. Figure 6As shown. In such embodiments, the input end 612A and the output end 612B of the amplifier waveguide 612 may be angled waveguides. Thus, in a first assembled configuration, the laser waveguide 608 of the gain chip 606 may be angled relative to the rear face 606A, and straight and perpendicular relative to the front face 606B, and the SOA 610 may include angled waveguides at both of its end faces (i.e., the input face 610A and the output face 610B).

[0064] In a first assembly configuration, the output of the low-reflection normal front facet 606B of the gain chip 606 can be coupled to the angled input of the SOA 610. That is, the output end 608B of the laser waveguide 608 of the gain chip 606 can be optically coupled to the angled input end 612A of the amplifier waveguide 612 of the SOA 610. In one embodiment, the two chips, namely the gain chip 606 and the SOA 610, can be tightly coupled to each other. In various embodiments, the gain chip 606 and the SOA 610 can be tightly coupled to each other through a lens. In one example, a microlens can be used to optically couple the output end 608B of the laser waveguide 608 of the gain chip 606 to the input end 612A of the amplifier waveguide 612 of the SOA 610. In Figure 6 In the various embodiments shown, the SOA 610 can be oriented relative to the gain chip 606 such that the optical axis 620 of the gain chip 606 can be aligned with the input optical axis 622 of the SOA 610. The input optical axis 622 of the SOA 610 can refer to the optical axis of the input end 612A (or input waveguide portion) of the amplifier waveguide 612. In such embodiments, the optical axis 620 of the gain chip 606 can be co-linear with the input optical axis 622 of the SOA 610. In order to guide the light 616 emitted by the gain chip 606 into the input end 612A of the amplifier waveguide 612 of the SOA 610, the SOA 610 can be tilted to allow its input optical axis 622 to match the optical axis 620 of the gain chip 606 from its low-reflection normal front facet 606B. For example, due to the tilted input end 612A of the amplifier waveguide 612, the SOA 610 can be tilted such that its input optical axis 622 matches the optical axis 620 of the gain chip 606. In various embodiments, the angle of the input end 612A of the amplifier waveguide 612 can be configured to be small, so that the tilt angle between the gain chip 606 and the SOA 610 can also be small to achieve low-loss optical coupling. Low-loss optical coupling can allow the gain chip 606 to be coupled to the SOA 610 with minimal optical power loss, thereby allowing the light 616 to be transmitted from the gain chip 606 to the SOA 610 with high efficiency, thereby ensuring that a large portion of the light 616 can be retained during the coupling process.

[0065] The gain chip-based ECL 602 may emit light 616 having a narrow line width at an initial output power. The SOA 610 may receive the light 616 emitted by the gain chip-based ECL 602 at an input face 610A, amplify the received light 616 as it propagates from the input face 610A to the output face 610B along an amplifier waveguide 612 of the SOA 610, and emit amplified light 618 from the output face 610B. The SOA 610 may control the resulting output power of the emitted amplified light 618 to a configurable level while keeping the narrow line width in the emitted amplified light 618 constant. The SOA 610 may also keep the laser wavelength of the gain chip-based ECL 602 constant while controlling the resulting output power of the emitted amplified light 618 to a configurable level.

[0066] Figure 7 is a schematic diagram showing an integrated device 700 according to an embodiment of the present disclosure, the integrated device including a gain chip-based ECL 702 and an SOA 710 arranged in a second assembly configuration. Figure 7 In the illustrated embodiment, the gain chip based ECL 702 may include a reflector 704 (e.g., a mirror) and a gain chip 706 in an external optical cavity. The external optical cavity may define the emission wavelength of the gain chip based ECL 702 and help stabilize and narrow the optical width of the laser output. The external optical cavity may also provide feedback to the gain chip 706 and may be adjusted to tune the laser output.

[0067] The gain chip based ECL 702 may be used as a narrow line width laser source configured to emit light 716 having a narrow line width at an initial output power. The gain chip 706 of the gain chip based ECL 702 may include a rear facet 706A, a front facet 706B, and a laser waveguide 708 extending from the rear facet 706A to the front facet 706B. In an embodiment, the laser waveguide 708 is substantially perpendicular to the rear facet 706A and the front facet 706B of the gain chip 706. The laser waveguide 708 may include a rear end 708A and an output end 708B. In an embodiment, the rear end 708A of the laser waveguide 708 may be at an angle relative to the rear facet 706A of the gain chip 706, such as Figure 7 In such an embodiment, the rear end 708A of the laser waveguide 708 may be an inclined waveguide. In other embodiments, the output end 708B of the laser waveguide 708 may be perpendicular to the front end face 706B of the gain chip 706, such as Figure 7 In such an embodiment, the output end 708B of the laser waveguide 708 may be a straight waveguide.

[0068] The gain chip 706 of the gain chip based ECL 702 can be integrated with the SOA 710, such as Figure 7As shown. In an embodiment, the gain chip 706 can be based on a face reflectivity of anti-reflection on the tilted rear facet 706A and a face reflectivity of low reflection on the normal front facet 706B. In another embodiment, the gain chip based ECL 702 is formed by coupling the light output 714 from the anti-reflection tilted rear facet 706A of the gain chip 706 to the reflector 704. Then, the light 716 can be emitted from the low reflection normal front facet 706B of the gain chip 706 to be coupled into the SOA 710.

[0069] In addition, the SOA 710 may include an input face 710A, an output face 710B, and an amplifier waveguide 712 extending from the input face 710A to the output face 710B. In an embodiment, the amplifier waveguide 712 is substantially perpendicular to the input face 710A and the output face 710B of the SOA 710. The amplifier waveguide 712 may include an input end 712A and an output end 712B. The input end 712A of the amplifier waveguide 712 may refer to an input waveguide portion of the amplifier waveguide 712. The output end 712B of the amplifier waveguide 712 may refer to an output waveguide portion of the amplifier waveguide 712. In various embodiments, the input end 712A of the amplifier waveguide 712 may be perpendicular to the input face 710A of the SOA 710, such as Figure 7 In such an embodiment, the input end 712A of the amplifier waveguide 712 may be a straight waveguide. In another embodiment, the output end 712B of the amplifier waveguide 712 may be angled relative to the output face 710B of the SOA 710, such as Figure 7 As shown. In such an embodiment, the output end 712B of the amplifier waveguide 712 may be a tilted waveguide. Thus, in the second assembly configuration, the laser waveguide 708 of the gain chip 706 may be angled relative to the rear facet 706A and straight and perpendicular relative to the front facet 706B, while the SOA 710 may include a straight waveguide at its input facet 710A and a tilted waveguide at its output facet 710B.

[0070] In a second assembly configuration, the output from the low-reflection normal front facet 706B of the gain chip 706 can be coupled into the direct input of the SOA 710. That is, the output end 708B of the laser waveguide 708 from the gain chip 706 can be optically coupled into the direct input end 712A of the amplifier waveguide 712 of the SOA 710. Figure 7In the various embodiments shown, the SOA 710 can be oriented relative to the gain chip 706 such that the optical axis 720 of the gain chip 706 can be aligned with the input optical axis 722 of the SOA 710. The input optical axis 722 of the SOA 710 can refer to the optical axis of the input end 712A (or input waveguide portion) of the amplifier waveguide 712. In such embodiments, the optical axis 720 of the gain chip 706 can be colinear with the input optical axis 722 of the SOA 710. In a second assembled configuration, the input end 712A of the amplifier waveguide 712 of the SOA 710 can be modified to be straight to allow the input end 712A to receive the light 716 from the gain chip 706 without any tilting of the SOA 710. In the second assembled configuration, no tilting of the SOA 710 relative to the gain chip 706 is required because the optical axes 720 and 722 of the chip are both perpendicular to their respective end faces, namely the front face 706B and the input face 710A. In one embodiment, the anti-reflection requirement of the input face 710A of the SOA 710 is achieved by coating an anti-reflection coating on the straight input face 710A of the SOA 710 .

[0071] The gain chip-based ECL 702 may emit light 716 having a narrow line width at an initial output power. The SOA 710 may receive the light 716 emitted by the gain chip-based ECL 702 at an input facet 710A, amplify the received light 716 as it propagates from the input facet 710A to the output facet 710B along an amplifier waveguide 712 of the SOA 710, and emit the amplified light 718 from the output facet 710B. The SOA 710 may control the resulting output power of the emitted amplified light 718 to a configurable level while maintaining a constant narrow line width in the emitted amplified light 718. The SOA 710 may also maintain a constant laser wavelength of the gain chip-based ECL 702 while controlling the resulting output power of the emitted amplified light 718 to a configurable level.

[0072] Those skilled in the art will appreciate that for the sake of brevity, Figure 3-5A and Figure 6-7 Various assembly configurations are shown in FIG. However, in various embodiments, other different assembly configurations may be implemented using different narrow linewidth laser sources, optical amplifiers, and different waveguide structures dedicated to similar or different functions.

[0073] Figure 8 FIG. 8 is a flow chart 800 illustrating a method for controlling the resulting output power of the emitted amplified light 110 to a configurable level while maintaining a constant narrow line width in the emitted amplified light 110 according to an embodiment of the present disclosure. Figure 1 , Figure 3-5A and Figure 6-7At 802, the SOA 106 may receive light 108 having an initial output power with a narrow line width from a laser source, such as a narrow line width laser source 104 (e.g., a DFB laser 302, 402, or 502), a gain chip based ECL 602 or 702, or the like. At 804, the SOA 106 may amplify the received light 108. At 806, the SOA 106 may emit the amplified light 110. At 808, the SOA 106 may control the resulting output power of the emitted amplified light 110 to a configurable level while maintaining a constant narrow line width in the emitted amplified light 110. In one embodiment, the SOA 106 may also maintain a constant laser wavelength of the laser source 104 while controlling the resulting output power of the emitted amplified light 110 to a configurable level.

[0074] Fig. 9 FIG. 9 is a flow chart 900 illustrating the operation of the optical amplifier 106 in the integrated device 102 under forward bias and reverse bias according to an embodiment of the present disclosure. Figure 1 , Figure 3-5A and Figure 6-7 1. At 902, an optical amplifier 106 (e.g., an SOA) may receive a voltage from a controller 114 operatively coupled to the optical amplifier 106. At 904, it may be determined whether the optical amplifier 106 is operating under forward bias. If the optical amplifier 106 is operating under forward bias, then at 906, the optical amplifier 106 may receive light 108 having an initial output power with a narrow line width from a laser source, such as a narrow line width laser source 104, such as a DFB laser 302, 402, or 502, a gain chip-based ECL 602 or 702, etc. At 908, the optical amplifier 106 may amplify the received light 108. At 910, the optical amplifier 106 may emit amplified light 110. At 912, the optical amplifier 106 may control the resulting output power of the emitted amplified light 110 to a configurable level while maintaining the narrow line width in the emitted amplified light 110 and the laser wavelength of the laser source 104 constant. If the optical amplifier 106 is operated under reverse bias, the optical amplifier 106 may act as a light absorber at 914. The optical amplifier 106 may then suppress the received light 108 having a narrow beam width at 916 without changing the drive current of the laser source 104. In one embodiment, the controller 114 may be operably coupled to the optical amplifier 106 and configured to control the bias of the optical amplifier 106.

[0075] By integrating the narrow linewidth laser source 104 with an optical amplifier 106 (interchangeably referred to as "SOA 106"), in one embodiment, the SOA 106 can also realize an alternative function as a shutter or an on / off switch. When the SOA 106 is biased at 0 volts (V) or reverse biased, the SOA 106 can be used as a light absorber, which is configured to substantially absorb or suppress the output light 108, thereby enabling the output light 108 with a narrow linewidth to be extinguished without changing the driving current to the narrow linewidth laser source 104. If the output of the narrow linewidth laser source 104 is turned off by cutting off its driving current, when the narrow linewidth laser source 104 is turned on again, it may take some time for the output to stabilize at the narrow linewidth. In the integrated device 102 including the narrow linewidth laser source 104 with the SOA 106, the time required to establish a stable narrow linewidth can be eliminated.

[0076] The present disclosure may be best understood with reference to the detailed drawings and descriptions described herein. Various embodiments are discussed below with reference to the drawings. However, it will be readily appreciated by those skilled in the art that the detailed descriptions provided herein with respect to the drawings are for illustrative purposes only, as the methods and systems may extend beyond the described embodiments. In one example, the teachings presented and the needs of a particular application may produce a variety of alternative and suitable methods to implement the functions of any detail described herein. Therefore, any method may extend beyond the specific implementation selections in the embodiments described and shown below.

[0077] Technology consistent with the present disclosure provides, among other features, an apparatus and method for controlling and stabilizing the output power of a narrow linewidth laser source 104 without any effect on the narrow linewidth and laser wavelength of the narrow linewidth laser source 104. Although various embodiments of the disclosed apparatus and method have been described above, it should be understood that they are for illustrative purposes only and not limiting. The foregoing examples and illustrative implementations of the various embodiments are for explanation only and should in no way be interpreted as limiting the present disclosure to the precise form disclosed. In addition, although the embodiments are described herein with reference to specific means, materials, techniques, and implementations, the embodiments herein are not intended to be limited to the details disclosed herein; rather, the embodiments extend to all functionally equivalent structures, methods, and uses, such as within the scope of the appended claims.

[0078] Although the present disclosure is described with reference to various embodiments, it will be appreciated by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the present disclosure. In addition, many modifications and variations may be made to adapt specific circumstances or materials to the teachings of the present disclosure, or may be obtained from practicing the present disclosure without departing from its scope. Therefore, the present disclosure is not limited to the disclosed embodiments, but the present disclosure will include all embodiments within the scope of the appended claims.

Claims

1. An integrated device, characterized in that: include: a laser source configured to emit light having a narrow beam width at an initial output power; as well as an optical amplifier operably coupled to the laser source, wherein the optical amplifier is configured to: receiving light from the laser source; amplifies the received light; emitting the amplified light; and The resulting output power of the emitted amplified light is controlled to a configurable level while keeping the narrow line width in the emitted amplified light constant.

2. The integrated device according to claim 1, characterized in that: The optical amplifier is a semiconductor optical amplifier.

3. The integrated device according to claim 1, characterized in that: The optical amplifier is further configured to maintain a constant laser wavelength of the laser source while controlling a resulting output power of the emitted amplified light to a configurable level.

4. The integrated device according to claim 1, characterized in that The laser source includes a laser waveguide extending from a front facet to a rear facet of the laser source, and The optical amplifier includes an amplifier waveguide extending from an input face to an output face of the optical amplifier.

5. The integrated device according to claim 4, characterized in that: The laser waveguide is substantially perpendicular to the front and rear facets of the laser source.

6. The integrated device according to claim 4, characterized in that: The laser waveguide comprises: a rear end configured to be perpendicular to a rear end face of the laser source; and The output end is configured to be perpendicular to the front end face of the laser source or to form a certain angle relative to the front end face of the laser source.

7. The integrated device according to claim 6, characterized in that: The output end of the laser waveguide is a straight active waveguide or a passive tilted waveguide.

8. The integrated device according to claim 7, characterized in that: The passive tilted waveguide is configured as a spot size converter aligned with an optical mode of the optical amplifier.

9. The integrated device according to claim 4, characterized in that: The amplifier waveguide is substantially perpendicular to the input face and the output face of the optical amplifier.

10. The integrated device according to claim 4, characterized in that The amplifier waveguide comprises: an input end, which is arranged to be perpendicular to the input face of the optical amplifier or to form a certain angle relative to the input face of the optical amplifier; and The output end is configured to form a certain angle relative to the output face of the optical amplifier.

11. The integrated device according to claim 10, characterized in that The input end of the amplifier waveguide is a straight waveguide or a tilted waveguide.

12. The integrated device according to claim 10, characterized in that Also included is an anti-reflection coating on an input end at the input end face of the optical amplifier and an output end at the output end face of the optical amplifier.

13. The integrated device according to claim 4, characterized in that The output of the laser waveguide is optically coupled to the input of the amplifier waveguide.

14. The integrated device according to claim 4, characterized in that The optical amplifier is oriented relative to the laser source such that an optical axis of the laser source is aligned with an input optical axis of the optical amplifier.

15. The integrated device according to claim 14, characterized in that The optical axis of the laser source is collinear with an input optical axis of the optical amplifier.

16. The integrated device according to claim 1, characterized in that Also included is at least one controller operably coupled to the laser source, wherein the at least one controller is configured to control the applied drive current to maintain an initial output power of the light.

17. The integrated device according to claim 1, characterized in that Also included is at least one controller operably coupled to the optical amplifier, wherein the at least one controller is configured to: change the optical gain of the optical amplifier to amplify the initial output power of the light from the laser source and stabilize the resulting output power to a configurable level.

18. The integrated device according to claim 1, characterized in that The optical amplifier is further configured to adjust for an optical power drift of an initial output power of the light from the laser source during control of a resulting output power of the emitted amplified light to a configurable level.

19. The integrated device according to claim 1, characterized in that The laser source is a narrow linewidth laser source selected from the group consisting of a distributed feedback laser and a gain chip based external cavity laser.

20. An integrated device, characterized in that: include: a laser source configured to emit light having a narrow beam width at an initial output power; and an optical amplifier operatively coupled to the laser source, the optical amplifier being operable in reverse bias and forward bias, wherein Based on forward bias operation, the optical amplifier is configured as: receiving light from the laser source; amplifies the received light; emitting the amplified light; and controlling the resulting output power of the emitted amplified light to a configurable level while maintaining a constant narrow line width in the emitted amplified light; and Based on reverse bias operation, the optical amplifier is configured as: operate as a light absorber; and The received light having a narrow light width is suppressed without changing the driving current of the laser light source.

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