Tunable single mode emitting semiconductor laser

Abstract

This invention provides a wide-tunable single-mode emitting semiconductor laser, comprising: a semiconductor substrate, a first linear ridge waveguide forming a first coupling cavity, and a second linear ridge waveguide forming a second coupling cavity, wherein the first coupling cavity is separated from the second coupling cavity by a gap. The first and second coupling cavities respectively include p-contacts and n-contacts for allowing laser currents I1 and I2 to be injected into the first and second coupling cavities. The first and second coupling cavities respectively include a first heating resistor and a second heating resistor, which are used to heat the first and second coupling cavities respectively when heating currents H1 and H2 are applied to them. The heating resistors are provided for heating the semiconductor substrate of the semiconductor laser to regulate the base temperature of the chip (i.e., the semiconductor substrate). T .

Description

[0001] Citation of prior patent applications under examination

[0002] This patent application claims the benefit of an earlier, pending U.S. Provisional Patent Application No. 63 / 004816, filed on 04 / 03 / 20 by AutomotiveCoalition For Traffic Safety, Inc. and Tim Koslowski et al., concerning a widely tunable single-mode emitting semiconductor laser (Attorney’s File No. ACTS-5 PROV), which is hereby incorporated herein by reference. Technical Field

[0003] This invention relates generally to lasers, and more particularly to wide-tunable single-mode emitting semiconductor lasers. Background Technology

[0004] Single-mode emitting semiconductor lasers provide light sources for a wide range of modern applications, from spectroscopy to telecommunications and far beyond. These single-mode emitting semiconductor lasers allow for electronic control of the light output and emission wavelength λ.

[0005] For many applications, it is ideal to have lasers spanning a distance λ. min ……λ max The wide tuning range of the emission wavelength, the width of which is determined by the tuning ratio. r To measure, among which, r yes:

[0006]

[0007] Typical semiconductor lasers emit many wavelengths; therefore, an additional wavelength selection mechanism is necessary to achieve single-mode operation (i.e., emitting a single wavelength λ). Wide-range wavelength selection mechanisms exist, but all-electronic wavelength selection mechanisms are typically limited to... r A tuning ratio of ≈0.01 or less. Wavelength selection mechanisms that support a wide wavelength range typically have a very large parameter space (i.e., they have a large number of tuning parameters), which complicates the characterization process and controlled operation of these wavelength selection mechanisms, and thus makes these approaches infeasible for mass production.

[0008] More specifically, semiconductor lasers without wavelength selection mechanisms emit light in many modes (i.e., at many wavelengths). For many applications, it is highly desirable to have a laser that emits only a single light mode (i.e., light at only a single wavelength). Many wavelength selection mechanisms exist, but generally, a monolithic (i.e., single-chip) wavelength selection mechanism is highly desirable. Monolithic solutions are preferred for several reasons, such as their size and their mechanical stability. Several monolithic wavelength selection mechanisms are known, such as distributed feedback (DFB) grids, distributed Bragg reflector (DBR) structures, and Vernier tuning of coupled cavities or resonators.

[0009] Often highly desirable is the construction of lasers with a wide tuning range for their wavelength. To achieve this, a wavelength selection mechanism is needed to control the wavelength. For many applications, a fully electronic wavelength selection mechanism is highly desirable. These mechanisms are typically based on tuning the refractive index of the laser's waveguide material using variations in (i) the temperature of the waveguide material and (ii) the density of the injected current. Optimal side-mode suppression ratios are achieved using lasers with distributed feedback (DFB) grids and lasers with distributed Bragg reflectors (DBR). With these wavelength selection mechanisms, tuning ratios up to 1% can be achieved under typical operating conditions (i.e., r ≈ 0.01).

[0010] Wider tuning ranges have been demonstrated whereby adjusting the wavelength selection mechanism (i.e., the DFB grating or DBR period) allows selection not only of a single wavelength but also of two or more preferred wavelengths. This makes it possible to construct multi-segment lasers such that absolute tuning of the effective refractive index of the waveguide material (achieved through variations in the waveguide material's temperature and the injection current density) substantially allows for continuous tuning of the output wavelength, and relative tuning (e.g., by selecting the phase relationship) allows for selection of the effectively switched-on grating or reflector. The combination of these two effects (continuous tuning and relative tuning) theoretically achieves a much higher tuning range, but in practice, as the tuning range increases, the fabrication and characterization complexity increases significantly.

[0011] One different approach to wavelength selection utilizes the Vernier effect. In this approach, two cavities are typically defined, each with its own Fabry-Perot wavelength comb. Tuning is then achieved by individually manipulating the refractive index of each cavity (i.e., by varying the temperature of the waveguide material and the density of the injected current). This selection is made within the range of the gain of the gain material used in the laser and encompasses both Fabry-Perot wavelength combs. This typically allows for a much wider tuning range than cases where wavelength selection is based on a DFB or DBR wavelength selection mechanism.

[0012] Therefore, known monolithic single-mode semiconductor lasers (i.e., DFB or DBR lasers) with high side-mode suppression ratios have a side-mode suppression ratio of approximately 1% (i.e., r A small tuning ratio (≈0.01). Lasers with DFB gratings or DBRs that can select more than one wavelength are typically very complex to operate. This makes the operating characteristics of the lasers highly susceptible to variations during fabrication. The desired protocol for finding operating parameters leads to very complex characterization processes in a high-dimensional parameter space (i.e., characterizing a specific waveguide material temperature and a specific injection current density for each segment of the laser is a highly complex procedure). This necessitates a characterization process requiring the collection of spectra on a fine grating in a high-dimensional parameter space. The number of elements in this grating increases exponentially with the number of independent parameters, making it infeasible to fabricate and control DFB or DBR lasers with the number of segments necessary for stable selection of many wavelengths.

[0013] Furthermore, known mechanisms that implement wavelength selection using the Vernier tuning principle suffer from similar problems: because it is desirable to simultaneously control the output wavelength, output intensity, and side-mode rejection ratio, numerous control parameters (especially waveguide material temperature and injection current density) are required. This, in turn, leads to a very complex characterization process in a very high-dimensional parameter space, making it impractical to mass-produce devices with fully simultaneous control of output wavelength, output intensity, and side-mode rejection ratio. Summary of the Invention

[0014] This invention provides a wide-tunable single-mode emitting semiconductor laser with fully electronic control over light intensity and an electronically tunable wavelength with a typical tuning ratio r ≈ 0.1 or greater, i.e., more than ten times the tuning ratio of conventional single-mode semiconductor lasers. In contrast to known devices with wide tuning ranges, the laser of this invention has a very simple characterization process and established process route, and is therefore suitable for mass production.

[0015] Generally, the present invention includes a monolithic semiconductor laser that provides single-mode light emission, a wide tuning range for wavelength, and simultaneous independent control of light intensity. The semiconductor laser is characterized by a semiconductor material comprising a layer structure suitable for laser emission, wherein two or more linearly aligned ridge waveguides are constructed thereon to provide two linearly aligned coupled cavities. Furthermore, the laser is characterized by: (i) individual controllability of three heating currents, wherein two power resistors are constructed very close to the two linear ridge waveguides, and one power resistor is mounted on the base of the chip (i.e., the monolithic semiconductor laser); and (ii) individual controllability of the laser current in the two coupled cavities. Additionally, the laser is characterized by the use of a gain material that provides wide gain tuning with temperature variations in the waveguide material.

[0016] More specifically, the present invention is based on the Vernier tuning principle, but the laser is constructed in such a way that the characterization process requires very few measured tuning parameters for each laser, while simultaneously enabling control of wavelength and light output with high side-mode suppression ratio.

[0017] A preferred embodiment of the invention includes a laser comprising two linearly arranged coupling cavities, each containing contacts for individually controlling the current of the two lasers (i.e., the injection current density for each coupling cavity). Additionally, the laser includes three heaters: the first two heaters are resistors constructed very close to the surfaces of the two coupling cavities, such that each resistor has effective thermal contact with only one of the two coupling cavities. The third heater is mounted on the bottom of the laser chip and allows control of the temperature of the laser chip body on a millisecond timescale.

[0018] A key observation about this design is that the wavelength of the mode is given by a simple relationship of the following form:

[0019]

[0020] in, a , b l , b 2. c l , c 2 represents the tuning parameters of the coupled cavity, which are described using the chip's basic temperature. T , where is the laser current with injection current density through the two coupled cavities. I l , I 2. And the heater current applied to the two coupled cavities through adjacent heating resistors of the two coupled cavities. H 1. H2-wavelength laser tuning. Fundamental wavelength. λ i It depends on the relative refractive indices of the two coupled cavities, and essentially only on the effective temperatures of the two coupled cavities. Note that the tuning parameters... a , b l , b 2. c l , c 2. For all basic patterns λ i They are all the same. Tuning parameters ( a , b l , b 2. c l , c 2 It can be measured by measuring the spectrum around a reference point; both the primary mode and the side modes will utilize tuning parameters ( a , b l , b 2. c l , c 2) To tune. After obtaining the tuning parameters ( a , b l , b 2. c l , c 2) Subsequently, the fundamental wavelength is measured by measuring the number of stages with a large step size. λ i The key point is that one needs to measure only a few tuning parameter lines with high precision to find the tuning parameters. a , b l , b 2. c l , c 2), and a rather coarse grid is used to locate the fundamental wavelength. λ i This significantly reduces the number of operating points that need to be characterized to characterize the laser. In this way, one can measure only five tuning parameters (i.e., a , b l , b 2. c l , c 2) and fundamental wavelength λ iLasers are characterized by a discrete set of fundamental wavelengths. The number of fundamental wavelengths depends on the laser's geometry and the specific application, and can range from as few as four to approximately 20 fundamental modes for a particular purpose. This allows for efficient characterization of the laser and thus facilitates the mass production of devices.

[0021] In conjunction with Equation 2 mentioned earlier, it should be realized that:

[0022] λ It is the target wavelength to which the laser is to be tuned, and is typically measured in nm.

[0023] λ i This is a specific fundamental wavelength (sometimes referred to as the fundamental mode in this text) previously determined for the laser, wherein this specific fundamental wavelength... λ i A specific combination of settings for T, I1, I2, H1, and H2 (which produces that specific fundamental wavelength) λ i ) is generated and is typically measured in nm;

[0024] 'a' is a coefficient typically measured in nm / Kelvin;

[0025] T is from the source used to generate the specific fundamental wavelength. λ i The temperature setting is a change in the chip's temperature, and is typically measured in Kelvin.

[0026] b1, b2, c1, and c2 are coefficients typically measured in nm / mA; and

[0027] I1, I2, H1, and H2 are used for specific fundamental wavelengths. λ i The changes in the injection current and heater current, where I1 and I2 are the injection currents for the first and second coupling cavities, respectively, and where H1 and H2 are the heater currents for the first and second coupling cavities, respectively, are all measured in mA.

[0028] Therefore, given a basic pattern for a specific combination of T, I1, I2, H1, and H2. λ i And the coefficients have been determined specifically for the laser. a , b l , b 2. c l as well as cIn case 2, the laser is moved from the known basic mode. λ i Tuning to the target wavelength λ This can be achieved by appropriately adjusting the values ​​of one or more of T, I1, I2, H1, and / or H2 so that the laser output can be adjusted from the fundamental wavelength. λ i Shift to target wavelength λ Of course, it will be appreciated that when one or more of T, I1, I2, H1 and / or H2 are adjusted, the refractive index of one or both of the coupling cavities may change, which may in turn require further changes in the values ​​of T, I1, I2, H1 and / or H2 in order to achieve the target wavelength. λ .

[0029] It will also be recognized that many combinations of T, I1, I2, H1, and H2 can be used to generate a given fundamental wavelength. λ i Furthermore, many different fundamental wavelengths can be identified for lasers with specific configurations. λ i In fact, it is possible to determine about five fundamental wavelengths. λ i Or in some cases, more fundamental wavelengths λ i (For a specific purpose, there may be up to twenty fundamental wavelengths) λ i To meaningfully characterize the laser. It will be realized that each specific fundamental wavelength... λ i It is generated by using a specific combination of T, I1, I2, H1, and H2, and the fundamental wavelength is selected accordingly. λ i The specific combination of T, I1, I2, H1, and H2 reflects factors related to the intended use of the laser.

[0030] Therefore, in use, when it is desired to tune the laser to a certain wavelength λ and the laser has been characterized to identify multiple fundamental wavelengths, λ i In this case, the user selects a wavelength close to the desired wavelength. λ Basic wavelength λ i And by setting the values ​​of T, I1, I2, H1, and H2 to generate the selected fundamental wavelength. λ i Those values ​​are used to set the laser to that fundamental wavelength. λ iAnd then the user adjusts T, I1, I2, H1 and / or H2 as needed so that the laser output is from the selected fundamental wavelength. λ i Move to the desired wavelength λ .

[0031] Two advantages of this invention over the prior art are that it provides a wide-tunable single-mode emitting semiconductor laser manufactured as a monolithic device, characterized by fully electronic simultaneous control of wavelength and optical output with a high side-mode suppression ratio. Monolithic devices are preferred because they are small, stable, and very robust when assembled in a suitable package. Fully electronic control is highly responsive (i.e., very fast), reliable, and can be achieved using relatively inexpensive and readily available electronic control equipment. In particular, wavelength tuning based on the cavity heater and laser current can be achieved in sub-millisecond timescales, while wavelength tuning based on the substrate heater can be achieved in millisecond timescales.

[0032] Another advantage of this invention over the prior art is that the laser achieves a wide tuning range while allowing tuning based on only five tuning parameters (i.e., those mentioned earlier in Equation 2). a , b l , b 2. c l , c 2) and several fundamental wavelengths (in Equation 2) λ i The measurement of ) is a fairly compact characterization process.

[0033] Another advantage of this invention stems from the use of a monolithic fabrication process: the laser can be easily integrated into a photonic integrated circuit, which can contain monolithic wavelength- and side-mode analyzers. Thus, a simplified characterization process allows for online calibration modes.

[0034] In a preferred embodiment of the present invention, a wide-tunable single-mode emitting semiconductor laser is provided, comprising:

[0035] Semiconductor substrate;

[0036] Substrate heater, used to heat semiconductor substrates;

[0037] A first linearly aligned ridge waveguide and a second linearly aligned ridge waveguide are formed on a semiconductor substrate. The first linearly aligned ridge waveguide and the second linearly aligned ridge waveguide are separated by a gap in order to form a first coupling cavity and a second coupling cavity.

[0038] A first ridge waveguide heater and a second ridge waveguide heater are used to heat the first linearly aligned ridge waveguide and the second linearly aligned ridge waveguide, respectively; and

[0039] The first p-contact and the second p-contact, respectively formed on the first linearly aligned ridge waveguide and the second linearly aligned ridge waveguide, and the first n-contact and the second n-contact, respectively communicating with the first linearly aligned ridge waveguide and the second linearly aligned ridge waveguide, are used to apply the first laser current and the second laser current to the first linearly aligned ridge waveguide and the second linearly aligned ridge waveguide, respectively.

[0040] In another preferred embodiment of the invention, a method for generating light of a selected wavelength is provided, the method comprising:

[0041] Provides a semiconductor laser, the semiconductor laser comprising:

[0042] Semiconductor substrate;

[0043] Substrate heater, used to heat semiconductor substrates;

[0044] A first linearly aligned ridge waveguide and a second linearly aligned ridge waveguide are formed on a semiconductor substrate. The first linearly aligned ridge waveguide and the second linearly aligned ridge waveguide are separated by a gap in order to form a first coupling cavity and a second coupling cavity.

[0045] A first ridge waveguide heater and a second ridge waveguide heater are used to heat the first linearly aligned ridge waveguide and the second linearly aligned ridge waveguide, respectively; and

[0046] The first p-contact and the second p-contact, respectively formed on the first linearly aligned ridge waveguide and the second linearly aligned ridge waveguide, and the first n-contact and the second n-contact, respectively communicating with the first linearly aligned ridge waveguide and the second linearly aligned ridge waveguide, are used to apply the first laser current and the second laser current to the first linearly aligned ridge waveguide and the second linearly aligned ridge waveguide, respectively.

[0047] Semiconductor lasers are characterized by the following equations:

[0048]

[0049] in, a , b l , b 2. c l , c 2 represents the tuning parameters of the first and second coupled cavities, which are described using the fundamental temperature of the semiconductor substrate. Tand are the laser currents, representing the injection current densities through the first and second coupling cavities, respectively. I l , I 2. And the heater currents applied to the first and second coupling cavities respectively through the first ridge waveguide heater and the second ridge waveguide heater. H 1 , H 2 Laser tuning; and

[0050] Adjust as necessary T , I l , I 2 and H 1 , H 2 At least one of them, so as to generate light of the selected wavelength. Attached Figure Description

[0051] These and other objects and features of the present invention will be more fully disclosed or become apparent from the following detailed description of preferred embodiments of the invention, which is to be described in conjunction with the appendix. Figure 1 Considering this, where the same number refers to the same component, and further wherein:

[0052] Figure 1-6 This is a schematic view showing a novel semiconductor laser mounted on a heat spreader;

[0053] Figure 7-10 It is shown Figure 1-6 Schematic view of further details of the novel semiconductor laser;

[0054] Figure 11 This is a schematic view showing the “zigzag” structure of two heating resistors used to heat the two coupled cavities of a novel semiconductor laser;

[0055] Figure 12 This is a schematic view illustrating mirror transmission in a laser;

[0056] Figure 13 This is a schematic view showing a typical spectrum of a coupled-cavity laser;

[0057] Figure 14 It is a schematic view showing a series of spectral side modes, in which the laser current varies through a short laser segment (i.e., a shorter coupling cavity), while all other operating parameters remain constant.

[0058] Figure 15This is a schematic view illustrating the optical tuning of the main side mode using the heater current of a short laser segment (i.e., a shorter coupled cavity); and

[0059] Figure 16 This is a schematic view showing optical tuning and gain tuning as linearly related to the base temperature of the laser chip. Detailed Implementation

[0060] In a preferred embodiment of the invention, and now viewed Figure 1-10 A wide-tunable single-mode emitting semiconductor laser 5 is provided, comprising a semiconductor substrate 10 having an epitaxial layer that allows the semiconductor laser to operate, for example, as a laser diode or as a cascaded laser. By way of example and not limitation, depending on the target wavelength range of the laser, the semiconductor substrate 10 may comprise an 111 / V semiconductor material, such as gallium nitride (GaN), gallium arsenide (GaAs), indium phosphide (InP), or gallium antimonide (GaSb). The epitaxial layer generally comprises a layer structure containing an active region having one or more quantum films, an upper cladding and a lower cladding, and an upper waveguide layer and a lower waveguide layer. More specifically, the wide-tunable single-mode emitting semiconductor laser 5 has a cubic shape, having a bottom formed by a semiconductor substrate 10 and a top formed by an upper waveguide layer, the upper waveguide layer being configured to provide two linearly aligned ridge waveguides 15, 20, the ridge waveguides 15, 20 being aligned on a line perpendicular to four facets 25, 30, 35, 40, wherein facets 25, 30 form the front and rear facets for the linear ridge waveguide 15, and facets 35, 40 form the front and rear facets for the linear ridge waveguide 20.

[0061] Two linear ridge waveguides 15, 20 preferably have a width and height comparable to the target wavelength, and are preferably spaced apart from each other by a distance D, approximately half the target wavelength. The two linear ridge waveguides 15, 20 are configured such that they guide the laser mode to four facets 25, 30, 35, 40. The two linear ridge waveguides 15, 20 define two coupling cavities 45, 50, respectively, wherein coupling cavity 45 includes facets 25, 30, and wherein coupling cavity 50 includes facets 35, 40. A gap 55 separates the two coupling cavities 45, 50.

[0062] The two linear ridge waveguides 15, 20 are preferably formed by a top-down material removal process (such as chemical or physical etching). The remaining material (i.e., the material remaining after etching) then defines the two linear ridge waveguides 15, 20. The lengths of the coupling cavities 45, 50 are typically defined by a second material removal process (typically etching) such that the facets 25, 30, 35, 40 and the gap 55 between the two linear ridge waveguides 15, 20 are defined with precision on the order of 10 nanometers. The typical lengths of the two coupling cavities 45, 50 are between approximately 80 nm and approximately 800 nm. It is also possible to construct distributed Bragg reflectors (DBRs) on the facets 25, 30, 35, 40 to control the reflectivity of the facets and gap 55 beyond values ​​that could be obtained using a single etching step.

[0063] Two heating resistors 60 and 65 are configured very close to the sides of two linear ridge waveguides 15 and 20, i.e., heating resistor 60 extends along linear ridge waveguide 15 and heating resistor 65 extends along linear ridge waveguide 20. The distance is typically one micrometer or a few micrometers (note: this refers to the lateral distance between linear ridge waveguides 15 and 20 and heating resistors 60 and 65, respectively - ideally, one would want these distances to be as close as possible, but the minimum distance is limited by the need to isolate heating resistors 60 and 65 from laser contacts (i.e., p-contacts 70 and 75, respectively, see below), so a distance of a few micrometers (e.g., two micrometers) is necessary). The two heating resistors 60 and 65 are typically made of highly conductive materials (e.g., titanium (Ti), platinum (Pt), or gold (Au)), and their dimensions are arranged such that the total resistance is on the order of a few ohms. Particularly preferred is that the heating resistors 60 and 65 have a “zigzag” structure, which enhances the thermal contact between the two linear ridge waveguides 15 and 20 and the two heating resistors 60 and 65 at a constant resistivity (see, for example, a schematic illustration of the aforementioned “zigzag” structure). Figure 11 ).

[0064] Laser 5 includes two p-contacts 70, 75 for receiving laser current on top of two linear ridge waveguides 15, 20, i.e., p-contact 70 extends along linear ridge waveguide 15 and p-contact 75 extends along linear ridge waveguide 20. The two p-contacts 70, 75 are typically treated with a highly conductive material (e.g., gold (Au)) and are respectively linked to two laser current contact pads 80, 85 (i.e., contact pad 80 is connected to p-contact 70 for linear ridge waveguide 15 and contact pad 85 is connected to p-contact 75 for linear ridge waveguide 20). The two laser current contact pads 80, 85 are positioned on the side of laser 5 opposite to the two heating resistors 60, 65. Two n-contacts 86, 87 for the two coupling cavities 45, 50 are located on the bottom of the chip (i.e., at the bottom of semiconductor substrate 10, see below) in a manner that those skilled in the art will recognize from this disclosure. Figure 7 The chip is processed. As an example and not a limitation, in a preferred form of the invention, the two n-contacts are a single shared n-contact, which is simply the bottom of the chip soldered to a heat sink (see heat sink 105 below, which has an integrated heating resistor 110 also described below). Individual currents are injected through p-contacts 70, 75 and, due to their size and relatively low lateral conductivity, do not widen before passing through the active layers (i.e., the gain medium in the linear ridge waveguides 15, 20).

[0065] The two heating resistors 60 and 65 preferably have their own contact pads on the side opposite to the laser current contact pads 80 and 85, and the two heating resistors 60 and 65 can share a common ground pad. By way of example and not limitation, the three heating resistor contact pads 90, 95, and 100 can be provided with a contact pad 95 serving as a common ground pad, such that contact pads 90 and 95 are used to supply current to heating resistor 60, and contact pads 100 and 95 are used to supply current to heating resistor 65.

[0066] The semiconductor substrate 10 of the laser 5 is preferably mounted on the plate of the heat sink 105, which includes a heating resistor 110 for heating the body of the semiconductor substrate 10. Contact pads 115 and 120 are used to supply current to the heating resistor 110.

[0067] If desired, contact pads 125, 130, 135, 140, and 145 can be disposed on heat sink 105, wherein the contact pads provide easy electrical connection to various components of semiconductor laser 5. For example, various contact pads among contact pads 125, 130, 135, 140, and 145 can be connected to contact pad 80 for p-contact 70 of coupling cavity 45, contact pad 85 for p-contact 75 of coupling cavity 50, contact pad 90 for heating resistor 60, contact pad 95 (common ground) for heating resistors 60 and 65, and various contact pads among contact pads 100 for heating resistor 65, thereby providing easy electrical connection to these components. Note that the various contact pads do not require a specific bonding scheme and can be adjusted according to specific applications. However, it is generally preferred that the common ground for heating resistors 60 and 65 is bonded to the ground for chip heating resistor 110. In other words, it is generally preferred that the contact pad 120 (ground) of the chip heating resistor 110 is connected to the contact pad 140 for the contact pad 95 (common ground) for the heating resistors 60 and 65.

[0068] Therefore, it will be seen that, in a preferred embodiment of the present invention, a semiconductor laser 5 is provided. The semiconductor laser 5 includes a semiconductor substrate 10, a first linear ridge waveguide 15 forming a first coupling cavity 45, and a second linear ridge waveguide 20 forming a second coupling cavity 50, wherein the first coupling cavity 45 and the second coupling cavity 50 are separated by a gap 55. The coupling cavities 45 and 50 include features for allowing laser current to flow. I 1 , I 2 P contacts 70 and 75 and n contacts (not shown, and preferably in the form of a common n contact) are injected into coupling cavities 45 and 50, respectively. Coupling cavities 45 and 50 also include heating resistors 60 and 65, which are used to adjust the heater current. H 1 , H 2 When heating resistors 60 and 65 are applied respectively, the coupling cavity is heated. Heating resistor 110 is provided to heat the semiconductor substrate 10 of the laser 5 in order to regulate the basic temperature of the chip (i.e., the semiconductor substrate 10). T .

[0069] The aforementioned structure provides the semiconductor laser 5 with five "controls" that can be used to adjust the output wavelength of the laser 5, namely, the basic temperature of the chip. T (It is controlled by the current through the heating resistor 110) laser current injected through the two coupling cavities 45, 50 (i.e., by means of the p-contact and n-contact for the two coupling cavities). I1 , I 2 and the heater current applied to the two coupling cavities through adjacent heating resistors 60 and 65. H 1 , H 2 .

[0070] In a preferred embodiment of the invention, the semiconductor laser 5 includes two coupled cavities 45 and 50, respectively heated by heating resistors 60 and 65. One of the coupled cavities 45 and 50 has a distance between the two in its Fabry-Perot modes that is less than the length of the tuning range. This is typically the shorter cavity (i.e., the one in which the laser is heated). Figure 1-10 Cavity 50 in the structure shown. Longer cavity (i.e., in...) Figure 1-10 The cavity 45 in the illustrated configuration can be several times longer than the shorter cavity 50. The two heating resistors 60, 65 are preferably in the range of 1-20 ohms. This ensures that the cavity can be heated at a voltage of less than 10 volts and a current of less than 500 mA. The semiconductor laser 5 is constructed on a semiconductor substrate 10 having its own heating resistor 110.

[0071] In a preferred embodiment of the invention, the semiconductor laser 5 is disposed (e.g., soldered) onto the heat sink 105.

[0072] The preferred operating modes of a laser are characterized according to Equation 2. Each shape of the fundamental mode has a distinct fundamental wavelength. λ i Then, it is possible to tune the heater current. H 1. H The combination of 2 is used to sweep the wavelength range. Afterwards, the fundamental temperature of the laser... T This is adjusted by changing the current of the heater that heats the semiconductor substrate (i.e., the chip). This shifts the maximum gain. The laser current is then adjusted. I 1 , I 2 This is necessary to achieve the desired light output level, because the laser efficiency is decisively dependent on the fundamental temperature of the chip (i.e., the semiconductor substrate 10). T Then, adjust the current of the two lasers. I 1 , I 2 The ratio between them is used to achieve the optimal edge mode suppression ratio.

[0073] Then, another sweep can be performed, for example, by increasing the heater current. H 1、H 2 This is performed by combining and varying the parameters. The process can be repeated until the entire gain of the laser material is covered. This allows the base temperature to be adjusted. T The advantage of fixing and then performing another sweep is that the tuning process is very fast because the slowest part of the tuning is achieved at the fundamental temperature of the chip (i.e., the semiconductor substrate 10). T Changes in aspects.

[0074] Additional information on the characterization of semiconductor lasers

[0075] 1. Background

[0076] There are multiple possibilities for constructing tunable semiconductor lasers capable of stable single-mode operation over a wide wavelength range. The suitability of these lasers for continuous production sets imposes many constraints, particularly:

[0077] 1. The established process: It must be an established process route that allows for high reproducibility and minimal process variation.

[0078] 2. Monolithic Devices: It is highly advantageous to manufacture monolithic devices in which the laser is composed of a single semiconductor chip. This avoids the expensive and fragile alignment steps during production.

[0079] 3. Fully electronic control: For field applications, it is highly ideal to achieve tuning through purely electronic control, which allows for the application of control electronics with relatively low cost.

[0080] 4. Simple Characterization: Widely tunable lasers possess a high-dimensional parameter space (fundamental temperature and various laser parameters, plus additional control currents). Direct characterization of this high-dimensional parameter space is impractical; for example, a five-dimensional parameter space scanned at a resolution of one percent in each parameter would require characterizing the laser at 10 billion operating points. Therefore, for continuous production, it is essential to have an efficient model of the laser governed by only a few parameters that can be easily and with sufficient accuracy measured.

[0081] 2. Valid Model

[0082] The examination of equilibrium states reveals that, in a given laser, these factors depend only on a small set of specific combinations of certain macroscopically attainable quantities. These quantities are central to the gain of the laser material. k o and width Δ k and the effective refractive index of the cavity segment n i These quantities essentially depend only on the laser chip and the laser itself. Ii and heater H i Basic temperature T The current level of the laser segment is a function of the laser's current level, i.e.

[0083]

[0084] And Δ k It is actually constant. A sufficiently good model for the maximum gain is:

[0085]

[0086] And assuming the gain width Δ k A constant value is actually sufficient. The effective refractive index of the laser segment can be described by the following:

[0087]

[0088] The effective refractive index of the gap is described by the following:

[0089]

[0090] Therefore, an effective model of a laser consists of the following: studying which optical modes of the laser (based on their vacuum wavenumber). The marker minimizes mirror loss while maximizing self-gain. k o Rising The modes that minimize mirror loss are the so-called Fabry-Perot modes. These are standing waves whose electric field modulus has a minimum at both laser facets. These modes are exponentially amplified by stimulated emission in the gain material, where the effective exponent is the gain length by which a single photon in this mode is reflected between the cavities. l g The average is given. See also Figure 12 For calculations of laser spectra, it is important to consider that a combination of one of the laser segments and the gap can be viewed as an optical element that facilitates coherent tunneling through one of the laser facets. This coherent tunneling has a periodic dependence on the vacuum wavenumber of the mode, and thus on the wavelength. Figure 13The transmission on the right facet for the right-shifting mode is schematically illustrated. A similar picture exists for the left-shifting mode on the left facet. A particular advantage of this design is that the reflectivities for both the left and right shifting components of the Fabry-Perot mode are identical due to the periodicity of the Fourier transform. This reduces the amount of characterization required to understand the Vernier point of the laser. The product of the reflectivities of the two facets allows one to calculate the effective number of gain lengths in which photons are retained in the laser, which is in turn the amplification exponent of the mode. Only the mode with the maximum amplification exponent will appear within the laser spectrum. This establishes a relationship between the model parameters and the laser spectrum at the operating point. Importantly, it is noted that one has an analytical expression for the wavelength dependence of the reflectivities of the two facets, and the reflectivity of each facet is well approximated by a periodic function of the wavenumber.

[0091] 3. Characterization

[0092] Identifying the mode with the highest reflectivity as the mode appearing in the laser's spectrum allows for efficient characterization of the laser by measuring several spectra. Identifying the tuning of the entire cavity by considering the sidemode spectrum of the laser is fairly straightforward. The Fabry-Perot modes of the entire laser behave as sidemodes of the coupled-cavity laser. The vacuum wavenumbers of the Fabry-Perot modes are:

[0093]

[0094] These patterns are Figure 13 The middle part is considered as the main mold and the side mold (with a value higher than -50). dB (The signal pattern). Using It was observed that the distance between the side modes was given by twice the laser length divided by the group index. The tuning parameters could be easily measured by measuring the number of times each laser parameter was varied. The tuning of the master mode (red / black) and the side modes (grayscale) was... Figure 14 The figure shows the laser current varying from 23 mA to 45 mA for a short laser segment (i.e., linear ridge waveguide 20), while other control parameters remain constant. The slope of this curve determines the tuning coefficient b2 for the current I2 in Equation 2. Figure 14 In the example, the tuning coefficient b2 has approximately 0.11. nm / mA The slopes of the principal mode and side modes). This slope represents the tuning parameter over the entire optical length tuned by the current. Similar tuning can be measured by varying the laser current through the long laser segment (i.e., the linear ridge waveguide 15), thus measuring the tuning parameter b1 of the long laser segment (for the current I1 in Equation 2). It is possible to directly obtain from Figure 13 and Figure 14Another important piece of information read: the intensity of the side modes within the gain region exhibits periodic modulation. Figure 14 In this context, the cycle is approximately 17. nm Furthermore, it can be observed that the tuning of the side modes is slower than that of the dominant mode. This is a resonant transmission effect of the optical length of the short cavity (i.e., the linear ridge waveguide 20). The dominant mode is considered to be located at the maximum value of the periodic reflectivity function of the short cavity (i.e., the linear ridge waveguide 20), which is approximately 41... mA The point intersects with the principal mode. This is the Vernier point, i.e., the point where the reflectivity of the combination of the two mirrors reaches its maximum. Using the tuning parameters and the periodicity of the reflectivity, we are now able to predict a large number of Vernier points.

[0095] For the heater current of linear ridge waveguides 15 and 20 H 1 and H 2 The tuning measurements are similar to those of the laser current. I 1 and I 2 Measurement. Figure 15 The tuning of the laser is depicted using variations in the heater current in the shorter linear ridge waveguide 20, with only the principal side modes plotted. It is clear that, as expected, the tuning is quadratic with respect to the heater current, since the heat generated by the heater is quadratically proportional to the current applied to the heater, and the tuning is linearly proportional to the temperature change caused by the deposited heat. This allows for consideration of the heater current in Equation 2. H 1 and H 2 And determine the tuning parameters c1 and c2.

[0096] The last piece of information needed to characterize a laser is to determine its gain tuning. This can be achieved by obtaining the temperature series. Figure 16 The laser is tuned by varying the fundamental temperature of the laser (i.e., by varying the current applied to the heating resistor 110), with only the principal side modes plotted. It is clear from the lines formed by the side modes that the optical tuning of the effective cavity length (i.e., the combined length of the linear ridge waveguide 15 and the linear ridge waveguide 20) is linearly proportional to temperature. Furthermore, the tuning of the laser's gain center can be read out by considering how the center of the principal mode, depicted in orange or red, lies on a line with a steeper slope. It is observed that the optical tuning is approximately... Gain tuning is approximately In this way, the tuning parameters can be determined for the variable T in Equation 2.

[0097] 4. Characterization of the new laser design compared with that of mass-produced lasers of the same design.

[0098] It should be recognized that there is typically a difference between the characterization of a newly designed laser and the characterization of a mass-produced laser of the same design. A new laser design typically requires detailed characterization because it is necessary to understand how process variations and material properties translate into effective model parameters. However, once the process variations of a particular design and process route are understood, and lasers of the same design are mass-produced, the characterization problem becomes much simpler. In this case, only "fine-tuning" needs to be measured. Thus, simple laser characterization can be reduced to even shorter procedures (but of the same type as those described above), which measure only a few properties of the laser to find the tuning parameters and position of the fundamental wavelength with sufficient accuracy.

[0099] Alternative construction and operation modes

[0100] Among the alternative configurations, one might consider lasers with more than two coupled cavities, lasers with only one heater at each coupled cavity, and lasers with several coupled cavities having heaters at each cavity or only at a subset of cavities. An important part of this design is that the mode equations for the optical modes possess proportional symmetry, allowing a simple formula, similar to that in Equation 2, to effectively describe the tuning behavior of the laser.

[0101] Among the alternative operating modes, the operating mode can be adjusted according to the needs of the application. In particular, it may be desirable to scan only a discrete set of wavelengths rather than performing multiple wavelength sweeps.

[0102] Modifications to the preferred embodiment

[0103] It should be understood that many additional changes to the details, materials, steps, and component arrangements described and illustrated herein for the purpose of explaining the nature of the invention can be made by those skilled in the art while still remaining within the principles and scope of the invention.

Claims

1. A wide-tunable single-mode emitting semiconductor laser, comprising: Semiconductor substrate; A substrate heater for heating the semiconductor substrate; A first linearly aligned ridge waveguide and a second linearly aligned ridge waveguide are formed on the semiconductor substrate, and the first linearly aligned ridge waveguide and the second linearly aligned ridge waveguide are separated by a gap in order to form a first coupling cavity and a second coupling cavity; A first ridge waveguide heater and a second ridge waveguide heater are respectively used to heat the first linearly aligned ridge waveguide and the second linearly aligned ridge waveguide; and A first p-contact and a second p-contact, respectively formed on the first linearly aligned ridge waveguide and the second linearly aligned ridge waveguide, and a first n-contact and a second n-contact, respectively communicating with the first linearly aligned ridge waveguide and the second linearly aligned ridge waveguide, are used to apply a first laser current and a second laser current to the first linearly aligned ridge waveguide and the second linearly aligned ridge waveguide, respectively. The heater current of the substrate heater and the heater currents of the first and second ridge waveguide heaters are individually controllable; and The first laser current and the second laser current can be controlled independently.

2. The tunable single-mode emitting semiconductor laser according to claim 1 further includes a heat sink, wherein, The semiconductor substrate is mounted to the heat sink, and further wherein the substrate heater is mounted to the heat sink.

3. The tunable single-mode emitting semiconductor laser according to claim 1, wherein, The semiconductor substrate is heated, the first linearly aligned ridge waveguide and the second linearly aligned ridge waveguide are heated, and a first laser current and a second laser current are applied to the first linearly aligned ridge waveguide and the second linearly aligned ridge waveguide, respectively, while controlling the output wavelength, output intensity and side-mode rejection ratio of the laser.

4. The tunable single-mode emitting semiconductor laser according to claim 1, wherein, The laser has a tuning ratio of r≈0.

1.

5. The tunable single-mode emitting semiconductor laser according to claim 1, wherein, The semiconductor substrate includes a layered structure suitable for laser emission.

6. The tunable single-mode emitting semiconductor laser according to claim 5, wherein, The layered structure includes a laser diode.

7. The tunable single-mode emitting semiconductor laser according to claim 1, wherein, The semiconductor substrate comprises a III / V semiconductor material selected from the group consisting of gallium nitride (GaN), gallium arsenide (GaAs), indium phosphide (InP), and gallium antimonide (GaSb).

8. The tunable single-mode emitting semiconductor laser according to claim 1, wherein, The first linearly aligned ridge waveguide and the second linearly aligned ridge waveguide have heights comparable to the target wavelength.

9. The tunable single-mode emitting semiconductor laser according to claim 1, wherein, The first linearly aligned ridge waveguide and the second linearly aligned ridge waveguide are separated from each other by a gap that is half the target wavelength.

10. The tunable single-mode emitting semiconductor laser according to claim 1, wherein, The first linearly aligned ridge waveguide and the second linearly aligned ridge waveguide have lengths between 80 nm and 800 nm.

11. The tunable single-mode emitting semiconductor laser according to claim 1, wherein, One of the first linearly aligned ridge waveguide and the second linearly aligned ridge waveguide has a longer length than the other of the first linearly aligned ridge waveguide and the second linearly aligned ridge waveguide.

12. The tunable single-mode emitting semiconductor laser according to claim 1, wherein, The first ridge waveguide heater and the second ridge waveguide heater include a tortuous structure.

13. A method for generating light of a selected wavelength, the method comprising: A semiconductor laser is provided, the semiconductor laser comprising: Semiconductor substrate; A substrate heater for heating the semiconductor substrate; A first linearly aligned ridge waveguide and a second linearly aligned ridge waveguide are formed on the semiconductor substrate, and the first linearly aligned ridge waveguide and the second linearly aligned ridge waveguide are separated by a gap in order to form a first coupling cavity and a second coupling cavity; A first ridge waveguide heater and a second ridge waveguide heater are respectively used to heat the first linearly aligned ridge waveguide and the second linearly aligned ridge waveguide; and A first p-contact and a second p-contact formed on the first linearly aligned ridge waveguide and the second linearly aligned ridge waveguide, respectively, and a first n-contact and a second n-contact communicating with the first linearly aligned ridge waveguide and the second linearly aligned ridge waveguide, respectively, are used to apply a first laser current and a second laser current to the first linearly aligned ridge waveguide and the second linearly aligned ridge waveguide, respectively. The semiconductor laser is characterized by the following equation: Where λ is the selected wavelength to which the semiconductor laser is to be tuned, λ i It is the fundamental wavelength. a , b l , b 2. c l , c 2 represents the tuning parameters of the first and second coupling cavities, which are described using the fundamental temperature of the semiconductor substrate. T The first laser current, representing the injection current density through the first coupling cavity and the second coupling cavity, are respectively... I l The second laser current I 2. And the heater currents applied to the first coupling cavity and the second coupling cavity respectively through the first ridge waveguide heater and the second ridge waveguide heater. H 1 , H 2 Laser tuning; and Adjustment T , I l , I 2 and H 1 , H 2 At least one of them, so as to generate light of the selected wavelength.

14. The method according to claim 13, wherein, The semiconductor laser is characterized by the following: Using the heater current H 1 , H 2 Combinations of these can be used to sweep the wavelength range; The fundamental temperature of the laser is adjusted by changing the current of the substrate heater. T This shifts the maximum gain. Adjust the current of the first laser I 1 The second laser current I 2 In order to achieve the desired light output level; Adjust the current of the first laser I 1 and the second laser current I 2 The ratio between them is used to achieve the optimal edge mode suppression ratio; By increasing the heater current H 1 , H 2 Combination variations to perform another sweep; and Repeat the steps above until the entire gain of the laser material is covered.

15. The method according to claim 13, wherein, The laser measures the fundamental wavelength. λ i The tuning parameters and discrete sets are used to characterize it.

16. The method according to claim 13, wherein, The number of fundamental wavelengths is between 4 and 20.

17. The method according to claim 13, wherein, The first linearly aligned ridge waveguide and the second linearly aligned ridge waveguide have heights comparable to the target wavelength.

18. The method according to claim 13, wherein, The first linearly aligned ridge waveguide and the second linearly aligned ridge waveguide are separated from each other by a gap that is half the target wavelength.

19. The method according to claim 13, wherein, The first linearly aligned ridge waveguide and the second linearly aligned ridge waveguide have lengths between 80 nm and 800 nm.

20. The method according to claim 13, wherein, One of the first linearly aligned ridge waveguide and the second linearly aligned ridge waveguide has a longer length than the other of the first linearly aligned ridge waveguide and the second linearly aligned ridge waveguide.

21. The method according to claim 13, wherein, The first ridge waveguide heater and the second ridge waveguide heater include a tortuous structure.

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