CN201298660Y - Monolithic-integrated, mode-hop-free, wavelength-tunable semiconductor laser - Google Patents

Abstract

The utility model discloses a single-chip integrated non-mode-hopping wavelength tunable semiconductor laser. It includes an optical cavity composed of a waveguide end face and a wavelength dispersion diffraction grating, an active waveguide placed on one side of the optical cavity to provide gain, and a wavelength dispersion diffraction grating placed on the other side of the optical cavity as a filter to select the emitted laser wavelength, active Between the waveguide and the wavelength dispersion diffraction grating is composed of a slab waveguide area and a wavelength tuning area, and the wavelength tuning area is sandwiched between a pair of electrodes. The wavelength of the grating filter is adjusted by changing the effective refractive index of the wavelength tuning region through an electrical effect, and the length of the optical cavity is adjusted at the same time, so that the adjustment of the laser mode wavelength is synchronized with the wavelength adjustment of the grating filter, thereby realizing continuous tuning without mode hopping . This design structure can be used for multi-band integrated tunable lasers and multi-wavelength tunable laser arrays.

Description

A monolithic integrated mode-hop-free wavelength-tunable semiconductor laser

technical field

The utility model relates to a semiconductor laser, in particular to a single-chip integrated non-mode-hopping wavelength tunable semiconductor laser.

Background technique

In many application fields such as interferometry, spectroscopy, and optical communication, it is hoped to obtain a wavelength-tunable laser source without mode-hopping covering a wide spectral range. The laser generally changes its output wavelength by adjusting the optical properties of the resonator, and when the optical properties of the resonator are continuously tuned, the excitation mode of the laser sometimes suddenly jumps from one wavelength to another, which is called mode hopping. Taking wavelength-scanning interferometry as an example, mode hopping can adversely affect the spatial resolution of distance measurements, positional accuracy, and other distance/depth-dependent properties. In order to realize mode-hop-free wavelength tuning, when the wavelength is tuned under the influence of a wavelength selection factor, the optical path length of the resonant cavity must also be tuned synchronously. Taking an external cavity tunable laser as an example, when the wavelength is adjusted by rotating the diffraction grating, it must be spatially displaced at the same time to ensure that the total cavity length contains the same number of wavelengths.

Compared with external cavity tunable lasers assembled from multiple discrete components, monolithic integrated semiconductor tunable lasers have more advantages. It's compact, low cost, and more reliable because it doesn't have any moving parts. A conventional monolithically integrated tunable laser usually includes a multi-electrode structure to achieve mode-hop-free tuning. Figure 1 is an example of prior art, a semiconductor tunable laser consists of a distributed Bragg reflection (DBR) grating (wavelength tuning element), an active gain region (laser generation), and a phase shift region (adjusting the length of the optical cavity) . Electrodes for electrical control are deposited on top of these three parts. When the reflection peak wavelength of the DBR grating is adjusted by the input current or load voltage, in order to prevent the mode hopping with the wavelength change, the phase shift region must be adjusted at the same time. Therefore, in order to achieve mode-hop-free wavelength tuning, two control circuits are required. The synchronization requirement for the two control units increases the complexity and cost of the equipment, and it can be very difficult to keep in sync due to factors such as the age of the lasers or environmental conditions.

In many application fields, it is also required that the laser wavelength is tuned so that it can cover two or more wavelength bands, or it can emit light waves of multiple wavelengths at the same time.

Contents of the invention

The purpose of the utility model is to provide a monolithic integrated semiconductor laser, which can realize wavelength tuning without mode-hopping through single-electrode control.

The technical scheme that the utility model solves its technical problem adopts is:

Solution 1: A monolithic integrated mode-hop-free wavelength tunable semiconductor laser includes an optical cavity composed of a waveguide end face and a wavelength dispersive diffraction grating, an active waveguide placed on one side of the optical cavity to provide gain, and placed on the other side of the optical cavity The side acts as a filter to select the wavelength dispersion diffraction grating for emitting laser wavelengths. The active waveguide and the wavelength dispersion diffraction grating are composed of a slab waveguide area and a wavelength tuning area. The wavelength tuning area is sandwiched between a pair of electrodes.

Any two optical paths emitted by the active waveguide and incident on two different positions on the wavelength dispersive diffraction grating will traverse the wavelength tuning region along their respective straight lines. The shape and size of the wavelength tuning region make any two straight lines in the wavelength tuning region The ratio of the optical path difference to the total optical path difference is a constant γ, which is equal to the ratio of the round-trip optical path of the optical path passing through the wavelength modulator region to the total round-trip optical path in the optical cavity.

The wavelength dispersion diffraction grating is a blazed grating.

When the wavelength tuning area is on the left side of the slab waveguide area, one end of the wavelength tuning area is the end O of the waveguide, and the boundary on the other side is the curve MB. The curve MB is determined by the formula Δlp=γΔLp, where ΔL _p =OP-OA, point O is the end point of the waveguide, A is the point closest to the end point O of the waveguide on the grating curve, M is any point on the line connecting OA, P is any given point on the grating; Δl _p =OQ-OM, OQ means along the OP The direction is the distance from point O to the boundary curve of the wavelength tuning area, and OM represents the distance from point O to the boundary curve of the wavelength tuning area along the OA direction; γ is a constant, which is the difference between the optical path difference in the wavelength tuning area and the total light in the optical cavity At the same time, each parameter needs to satisfy the relationship n _a L _a (l-OM)=n(OML-OAl).

When the wavelength tuning area is on the right side of the slab waveguide area, one end of the wavelength tuning area is the grating surface curve, and the boundary on the other side is the curve MB. The curve MB is formed by the formula Δlp=γΔLp, where ΔL _p =OP-OA, and point O is the waveguide , A is the closest point on the grating curve to the end point O of the waveguide, M is any point on the line connecting OA, P is any given point on the grating; Δl _p =PQ-AM, PQ means along the OP direction by The distance from point P to the boundary curve of the wavelength tuning area, AM represents the distance from point A to the boundary curve of the wavelength tuning area along the OA direction; γ is a constant, which is the optical path difference in the wavelength tuning area and the total optical path difference in the optical cavity ratio. At the same time, each parameter needs to satisfy the relationship n _a L _a (l-AM)=n(AML-OAl).

Solution 2: A monolithic integrated non-mode-hopping wavelength tunable semiconductor laser includes a partial reflective surface, an active waveguide combined with the partial reflective surface as a common waveguide, and a group of high reflective surfaces combined with the partial reflective surface to form an optical cavity Array, a set of active waveguide arrays combined with any one of a set of highly reflective surfaces and providing gain to the respective optical cavities when pumped; each active waveguide in a set of active waveguide arrays corresponds to A corresponding optical band, one for receiving a beam of light emitted by a group of active waveguide arrays, outputting the beam into the active waveguide as a common waveguide and as a filter to select a lasing wavelength in a certain band Wavelength dispersion diffraction grating; between the active waveguide and the wavelength dispersion diffraction grating is composed of a wavelength tuning area and a slab waveguide area; the wavelength tuning area is sandwiched between a pair of electrodes.

The shape of the wavelength tuning region enables the length of the optical cavity to be automatically adjusted when the lasing wavelength is adjusted to achieve no mode-hopping output; it is emitted by any waveguide in a group of active waveguide arrays and incident on two different positions on the wavelength dispersion diffraction grating Any two optical paths in the wavelength tuning region will traverse the wavelength tuning region along their respective straight lines. The shape and size of the wavelength tuning region make the ratio of the optical path difference between any two straight lines in the wavelength tuning region to the total optical path difference a constant. The constant is equal to the ratio of the round-trip optical path of the part of the optical path passing through the wavelength tuning area to the total round-trip optical path in the optical cavity.

An active waveguide as a common waveguide and a set of active waveguide arrays are set at specific positions so that the back diffraction efficiency of the wavelength dispersive diffraction grating at these positions is minimized, and at the same time the active waveguide as a common waveguide is minimized. The wavelength diffraction efficiency in the resonant cavity composed of the waveguide and a group of active waveguide arrays is maximized.

Solution 3: A monolithic integrated mode-hop-free wavelength tunable semiconductor laser includes an optical cavity composed of a waveguide end face and a wavelength dispersive diffraction grating, a group of active waveguide arrays placed on one side of the optical cavity to provide gain, placed in the optical cavity The other side is used as a filter to select the wavelength dispersion diffraction grating for emitting laser wavelengths. The active waveguide and the wavelength dispersion diffraction grating are composed of a slab waveguide area and a wavelength tuning area. The wavelength tuning area is sandwiched between a pair of electrodes.

The shape of the wavelength tuning region enables the length of the optical cavity to be automatically adjusted when the lasing wavelength is adjusted to achieve no mode-hopping output; it is emitted by any waveguide in a group of active waveguide arrays and incident on two different positions on the wavelength dispersion diffraction grating Any two optical paths in the wavelength tuning region will traverse the wavelength tuning region along their respective straight lines. The shape and size of the wavelength tuning region make the ratio of the optical path difference between any two straight lines in the wavelength tuning region to the total optical path difference a constant, The constant is equal to the ratio of the round-trip optical path of the part of the optical path passing through the wavelength tuning area to the total round-trip optical path in the optical cavity.

Compared with the background technology, the utility model has the beneficial effects of:

The utility model discloses a single-chip integrated non-mode-hopping wavelength tunable semiconductor laser. The laser can achieve continuous tuning of the outgoing laser without mode hopping. The laser has a wavelength tuning region of a specific shape and size, which is sandwiched between a pair of electrodes, and the effective refractive index of the region is changed by an electrical effect to adjust the wavelength of the grating filter, and at the same time adjust the length of the optical cavity, The adjustment of the wavelength of the laser mode is synchronized with the adjustment of the wavelength of the grating filter, so that continuous tuning without mode hopping can be realized through single-electrode control. In addition, the utility model can also be used for multi-band integrated tunable lasers and multi-wavelength tunable laser arrays.

Description of drawings

Fig. 1 is a semiconductor tunable laser in the background technology.

Fig. 2 is a wavelength demultiplexer based on an integrated blazed grating in the background technology.

Fig. 3 is a schematic diagram of the first structure of the integrated tunable laser of the present invention.

FIG. 4 is a cross-sectional view at OC in FIG. 3 .

Fig. 5 is a schematic diagram (a) of the spectral response of a grating filter and a schematic diagram (b) of the Fabry-Perot mode of the resonator.

Fig. 6 is a second structural schematic diagram of the integrated tunable laser of the present invention.

Fig. 7 is a schematic diagram of the third structure of the integrated tunable laser of the present invention.

Fig. 8 is a schematic diagram of an integrated tunable laser with multiple output bands based on the present invention.

Fig. 9 is a schematic diagram of a sinc-like diffraction envelope function, a specific position of an operating wavelength, and a position of a spurious wavelength to be suppressed.

Fig. 10 is a schematic diagram of an integrated tunable laser array based on the present invention.

In the figure: I, DBR grating, II, active gain region, III, phase shift region, G1, common waveguide, G2, active waveguide array, 1, active waveguide, 2, wavelength tuning region, 3, slab waveguide region , 4, blazed grating, 5, upper cladding, 6, core layer, 7, buffer layer, 8, substrate, 9, lower electrode, 10, upper electrode, 11, output waveguide, 12, input waveguide, 13, blazed grating , 14, single-mode fiber.

Detailed ways

Unlike conventional lasers that use DBR or DFR (distributed feedback) gratings to select working wavelengths, the device of the present invention selects wavelengths based on wavelength dispersion diffraction gratings, such as blazed gratings and arrayed waveguide gratings. At present, the waveguide diffraction grating technology is relatively mature, and can be used as a wavelength (de)multiplexer to be well applied in the DWDM system of optical communication.

Figure 2 is a schematic diagram of a typical wavelength demultiplexer based on an integrated diffraction grating, which includes an input/output waveguide array and a blazed grating. The input optical signals of different wavelengths are coupled into the input waveguide 12 of the demultiplexer by the optical fiber 14, and at the other end of the input waveguide, when the light enters the slab waveguide, it will diverge, enter the etched blazed grating 13 and then be reflected by the grating back into the slab waveguide. Light rays reflected according to the curvature of the grating will be converged to the entrance of the output waveguide 11 . Due to the dispersion properties of the diffraction grating, optical signals of different wavelengths are converged to different output waveguides 11 . For a given output waveguide, the selected optical signal wavelength depends on the effective refractive index of the slab waveguide and the geometric parameters of the grating.

Fig. 3 is a wavelength tunable laser of the present invention. It consists of the following parts: an active waveguide 1 (gain region), a blazed grating 4 (wavelength selection), a slab waveguide region 3 and a wavelength tuning region 2. The resonant cavity is composed of waveguide end face M and blazed grating.

FIG. 4 is a cross-sectional view of the slab waveguide region 3 and the wavelength tuning region 2 in FIG. 3 . The slab waveguide is composed of buffer layer 7, core layer 6 and upper cladding layer 5 and deposited on the substrate. A top electrode 10 is deposited on top of the wavelength tuning region. A metal lower electrode 9 is deposited on the bottom of the substrate 8 . The electrodes can change the refractive index of the waveguide in a certain way, such as injecting current into the slab waveguide or providing a controllable electric field.

The wavelength tuning region 2 has a specific structure based on the following design method, one end of which is the end point O of the active waveguide 1, and the boundary curve AB (Fig. 3) on the other side depends on the formula Δlp=γΔLp, where _ΔLp =OP- OA, point O is the end point of the active waveguide 1, A is the point closest to point O on the curve of the blazed grating 4, P is any given point on the blazed grating 4; Δl _p =OQ-OA, OQ means along the OP direction by The distance from point O to the boundary curve of the wavelength tuning area 2; γ is a constant, which determines the shape of the wavelength tuning area 2, and in order to achieve no mode-hop tuning, the constant must meet certain conditions. A detailed description of these conditions will be seen below.

The wavelength of the light wave that exits from point O and can be reflected by the blazed grating 4 and returns to point O must meet the following conditions:

$\mathrm{<span\; class="notranslate">\; \&Delta;\&Phi;</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; n\&Delta;</span>}{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}<span\; class="notranslate">\; +</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; l</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; g</span>}}\mathrm{<span\; class="notranslate">\; N\&pi;</span>}<span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

Where ΔΦ is the phase difference when light is reflected at point A and point P of the facet of the blazed grating, λ is the wavelength in vacuum, m _g is the diffraction order of the grating, and N is the grating period between point A and point P Number, n and n _t represent the refractive index of the slab waveguide region 3 and the wavelength tuning region 2, respectively.

Figure 5 shows that the waveguide has a Gaussian-like mode field profile. The blazed grating 4 and the active waveguide 1 form a spectral filter, which has a spectral response of a specific width. The passband of the spectral filter function may include multiple Fabry-Perot modes of the resonator (Figure 5). Assuming that the actual gain outside the passband is rather low, then the wavelength of the laser will be determined by the Fabry-Perot mode with the lowest loss in the passband. The wavelength of the Farby-Perot mode in the resonator composed of waveguide end face M and blazed grating is determined by the following formula:

$\frac{\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}<span\; class="notranslate">\; [</span>{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; nL</span>}<span\; class="notranslate">\; +</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; FP</span>}}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

n _a , L _a is the refractive index and length of the active waveguide 1, L is the distance between the end point O of the active waveguide 1 and the center C of the grating, and l is the length of the part where OC is located in the wavelength tuning region 2 (l =OD), m _FP is an integer corresponding to the Fabry-Perot modulus.

When the effective refractive index of the wavelength tuning region 2 is changed by the influence of current or voltage, the spectral response wavelength of the blazed grating 4 and the wavelength of the Farby-Perot mode will be adjusted. To avoid mode hopping, the two wavelengths must be tuned at the same speed. The tuning rate of the spectrum of the blazed grating 4 can be obtained by deriving from formula (1):

$\frac{\mathrm{<span\; class="notranslate">\; \&Delta;\&lambda;</span>}}{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&gamma;\&Delta;</span>}{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}}{\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; +</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; \&gamma;</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

where Δl _p = γΔL _p . For the same reason, formula (2) can get the tuning rate of Farby-Perot mode:

$\frac{\mathrm{<span\; class="notranslate">\; \&Delta;\&lambda;</span>}}{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}\mathrm{<span\; class="notranslate">\; l</span>}}{{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; nL</span>}<span\; class="notranslate">\; +</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; l</span>}}<span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

By equalizing the right side of formula (3)(4), we can get:

$\mathrm{<span\; class="notranslate">\; \&gamma;</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; nl</span>}}{{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; nL</span>}}<span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span>$

In order to realize mode-hopping-free operation, this condition determines the shape of the wavelength tuning region 2 in FIG. 3 . That is to say, when the effective refractive index of the wavelength tuning region 2 is changed by the influence of current or external electric field, the Farby-Perot mode and the spectral response of the blazed grating 4 will change synchronously.

In addition, point C is also on the surface of blazed grating 4, so Δlp=γΔLp is also satisfied at point C, namely $\mathrm{\&gamma;}=\frac{l-\stackrel{\&OverBar;}{\mathrm{OA}}}{L-\stackrel{\&OverBar;}{\mathrm{OA}}},$ Bring it into (5) to get n _a L _a (l-OA)=nOA (Ll)…………………………(6)

It can be seen that when the parameters of the blazed grating 4 and the active waveguide 1 are determined, the value of l can be obtained according to the formula, and then γ can be obtained.

The above discussion is the case where the endpoint on the boundary curve of the wavelength tuning area 2 coincides with the grating vertex A, and the general case will be discussed below.

As shown in FIG. 6 , the endpoint on the boundary curve of the wavelength tuning area 2 is any point M on OA. In this case, the above equations still hold true, but here Δl _p =OQ-OM, that is, the wavelength difference between the two optical paths in the wavelength tuning area 2, and the definitions of other parameters are the same as the above formulas, so the same as above can be obtained The γ expression of (5). In addition, since point C is also on the blazed grating 4 surface, Δlp=γΔLp is also satisfied at point C, and at this time $\mathrm{\&gamma;}=\frac{l-\stackrel{\&OverBar;}{\mathrm{om}}}{L-\stackrel{\&OverBar;}{\mathrm{OA}}},$ Bring it into formula (5) to get:

n _a L _a (l-OM)=n(OM·L-OA·l)………………………(7)

Comparing formulas (6) and (7), we can see that formula (6) is the special case of formula (7) when point M and point A coincide, and formula (7) is a general expression when M is any point on OA. For any case, the shape and size of the wavelength tuning region 2 can be determined as long as each parameter satisfies the above formula.

The above discussion is the case where the wavelength tuning area 2 is on the left side of the slab waveguide area 3 , and the wavelength tuning area 2 can also be placed on the right side, as shown in FIG. 7 , the wavelength tuning area 2 is on the right side of the slab waveguide area 3 . In this case, the above formulas still hold true, the difference is that Δl _p =PQ-AM here is still the wavelength difference between the two optical paths in the wavelength tuning area 2 . l=CD, which is the part of OC in the wavelength tuning region 2 . The definitions of other parameters are the same as the above formulas, so the same γ expression (5) can be obtained. In addition, since point C is also on the blazed grating 4 surface, Δlp=γΔLp is also satisfied at point C, and at this time $\mathrm{\&gamma;}=\frac{l-\stackrel{\&OverBar;}{\mathrm{AM}}}{L-\stackrel{\&OverBar;}{\mathrm{OA}}},$ Bring it into formula (5) to get:

n _a L _a (l-AM)=n(AM·L-OA·l)…………………………(8)

When the wavelength tuning region 2 is on the right side of the slab waveguide region 3, the shape and size of the wavelength tuning region 2 can be determined only if each parameter satisfies formula (8).

It can be seen from formula (3) that the wavelength adjustment range can be approximately expressed as $\frac{\mathrm{\&Delta;\&lambda;}}{\mathrm{\&lambda;}}\&ap;\frac{\mathrm{\&gamma;\&Delta;}{\mathrm{no}}_t}{\mathrm{no}}.$ In this way, a relatively large γ value will be obtained. In order to maximize the wavelength tuning range, a correspondingly large length of the wavelength tuning region 2 is required. The wavelength tuning range can be approximated as $\frac{\mathrm{\&Delta;\&lambda;}}{\mathrm{\&lambda;}}\&ap;\frac{\mathrm{\&Delta;}{\mathrm{no}}_t}{{\mathrm{no}}_t}\&Center\; Dot;\frac{\mathrm{nl}}{{\mathrm{no}}_a{L}_a+\mathrm{nL}},$ And less than Δn _t /n _t . Since the achievable refractive index change is about 0.1% in the case of reverse bias electro-optic effect, and about 1% in the case of current injection, the range of mode-hop-free tuning is generally one nanometer to several nanometers.

To cover a wider wavelength range or more bands, it can be achieved by multiple active waveguides, as shown in Figure 8. For a given wavelength, a corresponding active waveguide 1 in the array will be pumped. The central waveguide with the array of source waveguides is G2, while the active waveguide G1 is the common waveguide for all bands, which is always pumped. The resonant cavity is composed of a partially reflective surface M1 and a highly reflective surface M2. The output light is coupled into an optical fiber by the partially reflective surface M1. The output band can be changed by switching the active waveguides being pumped in the waveguide array. The central wavelength of the band corresponds to the given active waveguide G2 in the center of the array, which can be expressed as λ≈nΛ(sinθ ₁ +sinθ ₂ )/m _g , where Λ represents 4 periods of the blazed grating, θ ₁ and θ ₂ are active The included angle between the waveguides G1 and G2 and the normal at point C of the curve center of the blazed grating 4 (all active waveguides are aligned with the center C of the blazed grating 4).

When active waveguides G1 and an active waveguide in an array of active waveguides centered on G2 are pumped, other outgoing lasing wavelengths are possible due to the presence of other resonators: a partially reflective surface M1 is composed of blazed grating 4, and the other is composed of highly reflective surface M2 and blazed grating. The wavelengths generated by these resonant cavities can be obtained from the following formulas as λ ₁ ≈2nΛsinθ ₁ /m _g and λ ₂ ≈2nΛsinθ ₂ /mg respectively. In order to prevent multiple wavelengths from emitting at the same time, attention must be paid to the design of the demultiplexer. The end O1 of the common active waveguide G1 must be isolated from the active waveguide array. When their distance is far enough, the gain of the active waveguide 1 material at wavelength λ ₁ , λ ₂ will be much lower than that at wavelength λ. And the gain of λ is very close to the gain peak of the working band in the center of the material. Furthermore, the grating facets are blazed to maximize the transmission of the common active waveguide G1 to the central active waveguide G2 of the active waveguide array. The diffraction characteristics of a single grating surface determine that the diffraction envelope curve is a sinc-shaped curve. After optimizing the diffraction order of the blazed grating 4, that is, the geometric size of the grating surface, λ ₁ and λ ₂ can be close to the minimum intensity on the curve , while making λ close to the peak of the curve, as shown in Figure 9.

For some specific applications, it is sometimes necessary to emit multiple wavelengths simultaneously. This can also be realized by utilizing the structure of FIG. 8 , only need to simultaneously pump the active waveguides in two or more active waveguide arrays. Multiple wavelengths can be tuned simultaneously within each band. Taking optical communication as an example, if lasers with multiple wavelengths need to be directly tuned separately, then the common waveguide G1 of multiple lasers should be passive or have the lowest pump (and gain) so that different lasers can be tuned by crossing Gain modulation produces minimal crosstalk.

As shown in Figure 10, with a small modification to the design, the presently invented device can also be improved into an array of tunable lasers, each emitting a light wave of a different wavelength band. Different from the laser light of each wavelength in Fig. 8 being coupled into the same optical fiber at the partial reflection surface M1, the design structure in Fig. 10 needs to couple each excitation wavelength into multiple different optical fibers. Optimizing the blaze angle of the grating surface can make the light emitted by the central active waveguide be reflected by the blazed grating 4 and return to the original waveguide. Since the wavelength adjustment of each laser is realized by the same wavelength tuning area 2, they are strictly synchronized.

Using the current inventive idea, many other specific devices can be realized, for example, arrayed waveguide gratings can be used instead of blazed gratings.

Claims (10)

1. A monolithic integrated mode-hop-free wavelength tunable semiconductor laser, characterized in that: comprise an optical cavity made up of a waveguide end face (M) and a wavelength dispersion diffraction grating (4), place one side of the optical cavity to provide gain The active waveguide (1), the wavelength dispersion diffraction grating (4) placed on the other side of the optical cavity as a filter to select the wavelength of the emitted laser light, the active waveguide and the wavelength dispersion diffraction grating are composed of a flat waveguide area (3) and wavelength tuning region (2), the wavelength tuning region (2) is sandwiched between a pair of electrodes. 2. A monolithic integrated mode-hop-free wavelength tunable semiconductor laser according to claim 1, characterized in that: it is emitted by the active waveguide (1) and is incident on two different positions on the wavelength dispersion diffraction grating (4) Any two optical paths in the wavelength tuning region (2) will cross the wavelength tuning region (2) along their respective straight lines. The ratio of the path difference is a constant γ, which is equal to the ratio of the round-trip optical path of the optical path passing through the wavelength modulator region (2) to the total round-trip optical path in the optical cavity. 3. A monolithic integrated mode-hop-free wavelength tunable semiconductor laser according to claim 1, characterized in that: the wavelength dispersion diffraction grating (4) is a blazed grating. 4. A kind of monolithic integrated non-mode-hopping wavelength tunable semiconductor laser according to claim 1, characterized in that: when the wavelength tuning area (2) is on the left side of the slab waveguide area (3), the wavelength tuning area (2) ) is the end O of the waveguide, and the boundary on the other side is the curve MB. The curve MB is determined by the formula Δl _p = γΔL _p , where ΔL _p = OP-OA, the point O is the end point of the waveguide, and A is the distance from the waveguide on the grating curve. The nearest point of the end point O point of , M is any point on the OA line, P is any given point on the grating; Δl _p =OQ-OM, OQ represents along the OP direction from the O point to the boundary of the wavelength tuning area (2) The distance of the curve, OM represents the distance from the O point to the boundary curve of the wavelength tuning area (2) along the OA direction; γ is a constant, which is the ratio of the optical path difference in the wavelength tuning area to the total optical path difference in the optical cavity, each The parameters need to satisfy the relationship n _a L _a (l-OM)=n(OM·L-OA·l). 5. A monolithic integrated mode-hop-free wavelength tunable semiconductor laser according to claim 1, characterized in that: when the wavelength tuning area (2) is on the right side of the slab waveguide area (3), the wavelength tuning area (2) One end of ) is the grating surface curve, and the boundary of the other side is the curve MB. The curve MB is defined by the formula Δl _p = γΔL _p , where ΔL _p = OP-OA, point O is the end point of the waveguide, and A is the end point away from the waveguide on the grating curve The nearest point of the O point, M is any point on the OA line, and P is any given point on the grating; Δl _p =PQ-AM, PQ represents the distance from the P point to the wavelength tuning region (2) boundary curve along the OP direction Distance, AM represents the distance from point A to the boundary curve of the wavelength tuning area (2) along the OA direction; γ is a constant, which is the ratio of the optical path difference in the wavelength tuning area to the total optical path difference in the optical cavity, and each parameter needs to be The relationship n _a L _a (l−AM)=n(AM·L−OA·l) is satisfied. 6. A monolithic integrated mode-hop-free wavelength tunable semiconductor laser is characterized in that: an active waveguide (1) comprising a partial reflective surface (M1) combined with the partial reflective surface (M1) as a common waveguide, simultaneously Partially reflective surfaces (M1) combined to form an array of highly reflective surfaces (M2) for an optical cavity, combined with a set of highly reflective surfaces (M2) that provide gain for the respective optical cavity when pumped Active waveguide (1) array; each active waveguide (1) in a group of active waveguide (1) arrays corresponds to a corresponding optical waveband, and one is used to receive light emitted by a group of active waveguide (1) arrays A beam of light, the beam is output to the active waveguide (1) as a common waveguide and the wavelength dispersion diffraction grating (4) that selects a lasing wavelength in a certain wavelength band as a filter; the active waveguide (1) and the wavelength dispersion diffraction The grating (4) is composed of a wavelength tuning area (2) and a flat waveguide area (3); the wavelength tuning area (2) is sandwiched between a pair of electrodes. 7. A monolithic integrated non-mode-hopping wavelength tunable semiconductor laser according to claim 6, characterized in that: the shape of the wavelength tuning region enables the optical cavity length to be automatically adjusted when the lasing wavelength is adjusted so as to achieve no mode-hopping output ; Any two light paths that are emitted by any waveguide in a group of active waveguide (1) arrays and are incident on two different positions on the wavelength dispersion diffraction grating (4) will traverse the wavelength tuning region (2) along their respective straight lines ), the shape and size of the wavelength tuning area (2) make the ratio of the optical path difference of any two straight lines in the wavelength tuning area to the total optical path difference be a constant, the constant and the round trip of the optical path through the wavelength tuning area The ratio of the optical path to the total optical path in the optical cavity is equal. 8. A monolithic integrated mode-hop-free wavelength tunable semiconductor laser according to claim 6, characterized in that: an active waveguide (1) and a group of active waveguide (1) arrays as a common waveguide are set at specific positions, so that the back diffraction efficiency of the wavelength dispersive diffraction grating (4) at these positions is minimized, while making the The efficiency of wavelength diffraction in the co-constituent cavity is maximized. 9. A monolithic integrated mode-hop-free wavelength tunable semiconductor laser, characterized in that: comprising an optical cavity made up of a waveguide end face (M) and a wavelength dispersion diffraction grating (4), placed on one side of the optical cavity to provide gain A set of active waveguides (1) array, placed on the other side of the optical cavity as a filter to select the wavelength dispersion diffraction grating (4) between the active waveguide and the wavelength dispersion diffraction grating is composed of a flat waveguide area (3) and a wavelength A tuning region (2) is formed, and the wavelength tuning region (2) is sandwiched between a pair of electrodes. 10. A monolithic integrated non-mode-hopping wavelength tunable semiconductor laser according to claim 9, characterized in that: the shape of the wavelength tuning region enables the optical cavity length to be automatically adjusted when the lasing wavelength is adjusted so as to achieve no mode-hopping output ; Any two light paths that are emitted by any waveguide in a group of active waveguide (1) arrays and are incident on two different positions on the wavelength dispersion diffraction grating (4) will traverse the wavelength tuning region (2) along their respective straight lines ), the shape and size of the wavelength tuning area (2) make the ratio of the optical path difference of any two straight lines in the wavelength tuning area to the total optical path difference be a constant, the constant and the round trip of the optical path through the wavelength tuning area The ratio of the optical path to the total optical path in the optical cavity is equal.

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