WO2023145847A1

WO2023145847A1 - Method for improving organic semiconductor laser device, program, computer and organic semiconductor laser device

Info

Publication number: WO2023145847A1
Application number: PCT/JP2023/002544
Authority: WO
Inventors: Chihaya Adachi; Hyunsuk Park; Fatima Bencheikh; Ryutaro Komatsu; Takashi Fujihara
Original assignee: Kyushu University, National University Corporation; Koala Tech Inc.
Priority date: 2022-01-28
Filing date: 2023-01-27
Publication date: 2023-08-03
Also published as: TW202345480A

Abstract

An organic semiconductor laser device with a supercell structure composed of a first short-pitch periodic structure with length WS1, a long-pitch periodic structure with length WL and a second short-pitch periodic structure with length WS2 is improved by lengthening (WS1 + WS2), shortening WL, lengthening (WS1 + WL + WS2), or repeating the supercell structure.

Description

METHOD FOR IMPROVING ORGANIC SEMICONDUCTOR LASER DEVICE, PROGRAM, COMPUTER AND ORGANIC SEMICONDUCTOR LASER DEVICE

The present invention relates to a method for improving an organic semiconductor laser device.

In conventional sensing technologies such as 2D and 3D imaging (for example: bometric authentication) that project a known pattern of light called "structured light" on objects, a laser source with a diffractive optical element (DOE). The DOE are specially designed to split the single beam laser into multiple dotted beams to cover a large field of view, lines or other geometrical shapes of light. The DOE is a bulky element composed of lenses and waveguide. Thus, the use of DOE limits the miniaturisation and the integration density of such optical sensing system and increases the cost. Therefore, it is required to develop a laser device that can emit a split laser beam without using DOE.
On the other hand, in recent days, it has been disclosed that organic semiconductors have tremendous potential as a gain media. Organic semiconductor lasers (OSLs) are a fascinating device since they provide broad optical gain and fine wavelength tuning through a wide variety of molecular designs from blue to near-infrared regions with rather low lasing thresholds.^1-3 However, the current injection lasers, i.e., organic semiconductor laser diodes (OSLDs), are still at the very primitive stage and extensive developments have to be done from the aspect of both materials and device architectures. One of the critical issues of organic-based devices is the restriction of the film thickness. In order to realize the efficient carrier injection and transport in organic layers, thin-film structures such as a few hundred nm must be employed. Thus, we need to design the best optical resonator structures that fit the thin film-based OSLDs.
Optical resonators can play an essential role in improving the performances of organic lasers since they confine, amplify, and outcouple the light. There are several kinds of resonators such as Fabry-Perot⁴, distributed Bragg reflector (DBR) including vertical-cavity surface-emitting laser (VCSEL)⁵, and distributed feedback (DFB)⁶ structures. Among these resonators, DFB resonators are promising candidates for organic lasers.^7-9 A 1^st-order DFB resonator has been utilized in traditional inorganic semiconductor lasers, enabling planar direction feedback and laser emission.¹⁰ In addition, the 2^nd-order DFB resonator is also a good candidate owing to its surface emission. Further, a mixed-order DFB resonator has also been reported by combining the 1^st- and 2^nd-order resonators. Since the mixed-order DFB resonator combines the advantages of a 1^st-order (strong lateral feedback) and a 2^nd-order DFB resonator (partially light extraction as surface emission), the surface emission laser can be realized with a low threshold.¹¹
While such DFB structures provide rather low lasing thresholds, there is a critical issue in the control of emission angular distribution. For example, face recognition and time of flight (ToF) technologies require many high-density laser beam spots since the sensors can detect the geometry and reconstruct 3D spaces with high resolution (NPL 1).¹² However, this angular gap limits its application because the limited number of the light beams can be reflected against an object, exacerbating the sensing resolution. Similarly, this is also crucial for various kinds of display applications. Simultaneously, the current density threshold must be significantly reduced with the proper DFB structure design since organic gain materials are generally vulnerable under high power excitations both optically and electrically. Especially for electrically driven OSLDs, various annihilation processes such as singlet-triplet annihilation (STA) and triplet-triplet annihilation (TTA) are inevitable since a large amount of triplet generation, i.e., singlets and triplets with the formation ratio of 1:3, occurs under electrical pumping based on the well established spin statistics, and the long-lived triplets result in the strong quenching of the radiative singlets (NPL 2).¹³ Thus, reducing the threshold with the optimization of DFB structures is highly desirable to suppress these annihilations.

S. Zhou, and S. Xiao, HCIS 8, 1-27 (2018). C. Gartner, C. Karnutsch, U. Lemmer, and C. Pflumm, J. Appl. Phys. 101, 023107 (2007).

Under such situations, the inventors have performed earnest investigations with the aim of providing an organic semiconductor laser device exhibiting lower lasing threshold. Further, the inventors have performed earnest investigations with the aim of providing an organic laser device capable of emitting a split laser beam without using additional optical systems such as DOE.
As a result of earnest investigations for achieving the objects, the inventors have found that lasing threshold is lowered by providing two or more supercell structurers having first and second short-pitch periodic structures and long-pitch periodic structure in the optical resonator structure and controlling lengths in directions orthogonal to lattice grooves of each of the periodic structures. Further, the inventors have also found that a split laser beam having narrow angle difference between diffraction angles is realized by controlling of the lengths in directions orthogonal to lattice grooves of each of the periodic structures. The invention has been proposed based on the knowledge, and been achieved by the following means.

[1] A method for improving an organic semiconductor laser device comprising an optical resonator structure and a light amplification layer composed of an organic semiconductor, wherein:
the optical resonator structure has at least one supercell structure which has a first short-pitch periodic structure, a long-pitch periodic structure and a second short-pitch periodic structure,
the first short-pitch periodic structure is arranged adjacent to one end of the long-pitch periodic structure, and the second short-pitch periodic structure is arranged adjacent to the other end of the long-pitch periodic structure,
at least two of (i) a direction orthogonal to lattice grooves of the first short-pitch periodic structure, (ii) a direction orthogonal to lattice grooves of the long-pitch periodic structure and (iii) a direction orthogonal to lattice grooves of the second short-pitch periodic structure are on a straight line, and
the method comprises at least one of:
(1) lengthening (WS1 + WS2),
(2) shortening WL,
(3) lengthening (WS1 + WL + WS2), and
(4) repeating the supercell structure,
wherein WS1 represents a length in a direction orthogonal to lattice grooves of the first short-pitch periodic structure, WS2 represents a length in a direction orthogonal to lattice grooves of the second short-pitch periodic structure, WL represents a length in a direction orthogonal to lattice grooves of the long-pitch periodic structure.
[2] The method according to [1], conducting (1).
[3] The method according to [1], conducting (2).
[4] The method according to [1], conducting (3).
[5] The method according to [1], conducting (4).
[6] The method according to [1], conducting (1) and (2).
[7] The method according to [1], conducting (1) and (3).
[8] The method according to [1], conducting (2) and (3).
[9] The method according to [1], conducting (1), (2) and (3).
[10] The method according to any one of [6] to [9], further conducting (4).
[11] The method according to any one of [1] to [10], adjusting (WS1 + WS2) / WL to be 4 or more, for example 10 or more, for example 50 or more, for example 90 or more, for example 150 or more, for example 800 or more.
[12] The method according to any one of [1] to [11], adjusting (WS1 + WS2) to be 1 μm or more, for example 4 μm or more, for example 10 μm or more, for example 40 μm or more, for example 200 μm or more.
[13] The method according to any one of [1] to [12], adjusting WL to be 10 μm or less, for example 2 μm or less, for example 0.6 μm or less.
[14] The method according to any one of [1] to [13], adjusting (WS1 + WL + WS2) to be 2 μm or more, for example 5 μm or more, for example 20 μm or more, for example 50 μm or more, for example 250 μm or more.
[15] The method according to any one of [1] to [14], satisfying WS1=WS2.
[16] The method according to any one of [1] to [15], wherein all of (i) a direction orthogonal to lattice grooves of the first short-pitch periodic structure, (ii) a direction orthogonal to lattice grooves of the long-pitch periodic structure and (iii) a direction orthogonal to lattice grooves of the second short-pitch periodic structure are on a straight line.
[17] The method according to any one of [1] to [16], wherein the first short-pitch periodic structure is in contact with one end of the long-pitch periodic structure, and the second short-pitch periodic structure is in contact with the other end of the long-pitch periodic structure.
[18] The method according to any one of [1] to [17], wherein the periodic structure is a grating composed of ridges and grooves.
[19] The method according to [1] to [18], wherein the first short-pitch periodic structure and the second short-pitch periodic structure are first-order gratings, and the long-pitch periodic structure is a second-order grating.
[20] The method according to any one of [1] to [19], wherein the method is for lowering lasing threshold.
[21] The method according to any one of [1] to [19], wherein the method is for narrowing diffraction angle of laser emission.
[22] The method according to any one of [1] to [19], wherein the method is for lowering lasing threshold and narrowing diffraction angle of laser emission.
[23] The method according to any one of [1] to [22], wherein the method is for designing an organic semiconductor laser device.
[24] The method according to any one of [1] to [23], wherein the method is for evaluating an organic semiconductor laser device.
[25] The method according to any one of [1] to [24], wherein the method is for producing an organic semiconductor laser device.
[26] A program for conducting the method of any one of [1] to [25].
[27] A computer for conducting the method of any one of [1] to [25].
[28] An organic semiconductor laser device produced by the method of [1] to [25].
[29] An organic semiconductor laser device comprising an optical resonator structure and a light amplification layer composed of an organic semiconductor, wherein:
the optical resonator structure has at least one supercell structure which has a first short-pitch periodic structure, a long-pitch periodic structure and a second short-pitch periodic structure,
the first short-pitch periodic structure is arranged adjacent to one end of the long-pitch periodic structure, and the second short-pitch periodic structure is arranged adjacent to the other end of the long-pitch periodic structure,
at least two of (i) a direction orthogonal to lattice grooves of the first short-pitch periodic structure, (ii) a direction orthogonal to lattice grooves of the long-pitch periodic structure and (iii) a direction orthogonal to lattice grooves of the second short-pitch periodic structure are on a straight line, and
the organic semiconductor laser device has at least one of a lengthened (WS1 + WS2), a shortened WL, a lengthened (WS1 + WL + WS2) and two or more supercell structures, wherein WS1 represents a length in a direction orthogonal to lattice grooves of the first short-pitch periodic structure, WS2 represents a length in a direction orthogonal to lattice grooves of the second short-pitch periodic structure, WL represents a length in a direction orthogonal to lattice grooves of the long-pitch periodic structure.
[30] The organic semiconductor laser device according to [28] or [29], wherein the optical resonator structure has two or more supercell structures arranged so that directions orthogonal to lattice grooves of the two or more supercell structures are on a straight line.
[31] The organic semiconductor laser device according to [30], wherein WS1, WL and WS2 of the two or more supercell structures are the same.
[32] The organic semiconductor laser device according to [30], wherein the lengths in the directions orthogonal to lattice grooves of the two or more supercell structures are random.
[33] The organic semiconductor laser device according to any one of [30] to [32], wherein the optical resonator structure has 10 or more supercell structures.
[34] The organic semiconductor laser device according to any one of [28] to [33], wherein the first short-pitch periodic structure, the long-pitch periodic structure, and the second short-pitch periodic structure have grooves with a depth of less than 75 nm, for example 20 to 70 nm.
[35] The organic semiconductor laser device according to any one of [28] to [34], wherein the first short-pitch periodic structure, the long-pitch periodic structure, and the second short-pitch periodic structure have a distributed feedback (DFB) structure.
[36] The organic semiconductor laser device according to [35], wherein each distributed feedback (DFB) structure is selected from the group consisting of first order DFB structure, second order DFB structure, third order DFB structure and even higher order DFB structures.
[37] The organic semiconductor laser device according to any one of [28] to [36], wherein the first short-pitch periodic structure, the long-pitch periodic structure, and the second short-pitch periodic structure are composed of an insulating material.
[38] The organic semiconductor laser device according to any one of [28] to [37], wherein the first short-pitch periodic structure, the long-pitch periodic structure, and the second short-pitch periodic structure have periodically-arranged ridges composed of an insulating material on an insulating substrate.
[39] The organic semiconductor laser device according to [38], wherein the ridges and the insulating substrate are composed of different insulating materials.
[40] The organic semiconductor laser device according to [38], wherein the ridges are composed of silicon dioxide, and the insulating substrate is composed of a glass substrate.
[41] The organic semiconductor laser device according to any one of [38] to [40], wherein the surface of the insulating substrate is exposed at the bottom of the grooves.
[42] The organic semiconductor laser device according to any one of [28] to [41], further comprising an organic layer on a surface of the optical resonator structure.
[43] The organic semiconductor laser device according to [42], further comprising a transparent protective layer on a side opposite to the optical resonator structure of the organic layer.
[44] The organic semiconductor laser device according to [42] or [43], emitting a laser beam from the opposite side of the organic layer of the optical resonator structure.
[45] The organic semiconductor laser device according to [43], emitting a laser beam from the opposite side of the organic layer of the transparent protective layer.
[46] The organic semiconductor laser device according to any one of [28] to [45], emitting two or more types of diffracted light having different diffraction angles.
[47] The organic semiconductor laser device according to [46], wherein the angle difference between the diffraction angles of diffracted light having the closest emission direction among the two or more types of diffracted light is 8° or less, for example 7° or less, and 6° or less.
[48] The organic semiconductor laser device according to any one of [28] to [47], wherein the organic layer contains an organic compound having at least one stilbene unit.
[49] The organic semiconductor laser device according to any one of [28] to [48], wherein the organic layer contains 4,4 '- bis [ (N-carbazole) styryl ] biphenyl (BSBCz).
[50] The organic semiconductor laser device according to any one of [28] to [49], wherein the organic layer has a thickness of 80 to 350 nm, for example 100 to 300 nm, for example 150 to 250 nm.
[51] A device selected from the group consisting of a biosensor, a structured optical lighting device, an optical sensing device, and a face recognition device comprising the organic semiconductor laser device according to any one of [28] to [50].

Compatibility with all-organic platform and OLED technology, Monolithic integration of different laser colors together and also integration with electroluminescent devices and other organic devices, reduce the size of structured light based-sensors and optical sensors systems.

Fig.1 is a schematic plan view showing an example of the optical resonator structure used in the invention. Fig.2 is a schematic plan view showing an optical resonator structure having three or more supercell structures of varying length. Fig.3 is a simulation result of angular dependence of laser emission of a laser diode having the optical resonator structure shown in Fig. 2. Fig. 4 (a) is a scanning electron microscopy (SEM) image of 4:12 ratio of 2^nd- and 1^st-order sampled gratings in mixed-order DFB, (b) is a schematic plan view of 4:12, 4:36, and 4:200 ratio of 2^nd and 1^st order sampled gratings in mixed-order DFB (Λ_SC corresponds to one supercell length, which is sum of one 2^nd-order and two 1st-order sampled gratings), (c) is a cross-sectional view of organic semiconductor laser (OSL) device encapsulated with CYTOP and sapphire glass cover, (d) is a structural formula of 4,4’-bis[(N-carbazole)styryl]biphenyl (BSBCz) as gain media and 4,4’-di(N-carbazolyl)biphenyl (CBP) as host. Fig. 5 (a) to (c) are photonic band diagram (colored image) and PL spectra at θ=0° (right side) and far-field emission pattern (down side) of (a) 4:12 ratio, (b) 4:36 ratio, and (c) 4:200 (2nd:1st) ratio mixed-order DFB devices with 2nd order DFB (4 periods). Fig. 6 (a) to (c) are PL (black) and lasing (red) spectra of (a) 4:12 ratio, (b) 4:36 ratio, and (c) 4:200 ratio in mixed-order sampled DFB devices (No. 4, 5, and 6 in Table 1) taken by 0° emission, (d) is graph showing width of stopband and lasing threshold depending on the number of 1st-order periods in supercells. Fig. 7 is a schematic diagram of single angular measurement system. Fig. 8 is a schematic diagram of Fourier imaging spectroscopy system. Fig. 9 is an image showing beam shape of NL100 nitrogen laser. Fig. 10 an image showing beam shape of Nd:YAG laser. Fig. 11 is a graph showing spectra of UV-vis absorbance (blue line), photo luminescence (red line), and amplified spontaneous emission (black dashed line) of BSBCz:CBP (6 wt%) film. Fig. 12 (a) and (b) are graphs showing five second-order period lengths lasing property comparison with their (a) lasing spectrum and (b) lasing threshold. Fig. 13 (a) to (c) are scanning electron microscope (SEM) images of sampled mixed-order DFB with 4 periods of second DFB region (a) 1:3, (b) 1:9, and (c) 1:50 ratio. Fig. 14 (a) to (c) are graphs showing lasing threshold summary of sampled mixed-order DFBs with 4 periods of second DFB region (a) 1:3 (3 trials), (b) 1:9 (3 trials), and (c) 1:50 ratio (3 trials). Fig. 15 is a photonic band diagram of non-sampled 2^nd order DFB OSL. Fig. 16 (a) to (c) are photonic band diagram and its 0 ° cropped photo luminescence spectra (right side) and far-field emission pattern (down side) of 1 period of second order DFB regions and different ratios (a) 1:3 ratio, (b) 1:9 ratio, and (c) 1:50 ratio. Fig. 17 (a) to (c) are photonic band diagram and its 0 ° cropped photo luminescence spectra (right side) and far-field emission pattern (down side) of 36 periods of second order DFB regions and different ratios (a) 1:3 ratio, (b) 1:9 ratio, and (c) 1:50 ratio.

The contents of the invention will be described in detail below. The constitutional elements may be described below with reference to representative embodiments and specific examples of the invention, but the invention is not limited to the embodiments and the examples. In the present specification, a numerical range expressed by “from X to Y” means a range including the numerals X and Y as the lower limit and the upper limit, respectively.

Method for improving Organic Semiconductor Laser Device
The method of the invention is a method for improving an organic semiconductor laser device comprising an optical resonator structure and a light amplification layer composed of an organic semiconductor, wherein:
the optical resonator structure has at least one supercell structure which has a first short-pitch periodic structure, a long-pitch periodic structure and a second short-pitch periodic structure,
the first short-pitch periodic structure is arranged adjacent to one end of the long-pitch periodic structure, and the second short-pitch periodic structure is arranged adjacent to the other end of the long-pitch periodic structure,
at least two of (i) a direction orthogonal to lattice grooves of the first short-pitch periodic structure, (ii) a direction orthogonal to lattice grooves of the long-pitch periodic structure and (iii) a direction orthogonal to lattice grooves of the second short-pitch periodic structure are on a straight line, and
the method comprises at least one of:
(1) lengthening (WS1 + WS2),
(2) shortening WL,
(3) lengthening (WS1 + WL + WS2), and
(4) repeating the supercell structure,
wherein WS1 represents a length in a direction orthogonal to lattice grooves of the first short-pitch periodic structure, WS2 represents a length in a direction orthogonal to lattice grooves of the second short-pitch periodic structure, WL represents a length in a direction orthogonal to lattice grooves of the long-pitch periodic structure.
The method of the invention is for improving the properties of an organic semiconductor laser device. In one embodiment of the invention, the method is for lowering lasing threshold. In another embodiment of the invention, the method is for narrowing diffraction angle of laser emission. In one embodiment of the invention, the method is for lowering lasing threshold and narrowing diffraction angle of laser emission. The term "diffraction angle of laser emission" referred herein means the angle difference between the diffraction angles of two diffracted beams having the closest emission direction among the two or more types of diffracted beams with different diffraction angles. The narrower diffraction angle of laser emission, the more split the laser beam, and is more useful as a structured illumination device for detecting 3D geometry.
In the invention, the term "periodic structure" in "first short-pitch periodic structure", "long-pitch periodic structure" and "second short-pitch periodic structure" means a structure in which a plurality of lattice grooves is arranged side by side at a constant pitch. Hereafter, the convex part between adjacent lattice grooves is referred to as a "ridge". the periodic structure may be a grating in which a plurality of raised portions and a plurality of grating grooves are alternately arranged at a constant pitch.
In the invention, the "pitch" in "first short-pitch periodic structure", "long-pitch periodic structure " and "second short-pitch periodic structure " means the distance between the side surfaces of adjacent lattice grooves. In each of the supercell structures, the "long pitch periodic structure" is a periodic structure having a longer pitch than "first short-pitch periodic structure " and "second short pitch-periodic structure".
For a description of the organic semiconductor laser device used in the invention, the description in the paragraph "organic semiconductor laser device" above may be referenced.

Fig. 1 shows an optical resonator structure 10 having three or more supercell structures as an example of the optical resonator structure used in the invention. However, the optical resonator structure capable of being used in the invention is not construed as being limited to the example. In Fig. 1, "FSP" represents the first short-pitch periodic structure, "LP" represents the long-pitch periodic structure, and "SSP" represents the second short-pitch periodic structure. In the optical resonator structure 10, the distance Λ1 between the side surfaces of the adjacent lattice grooves 1a and 1b corresponds to the pitch of the first short-pitch periodic structure FSP, the distance ΛL between the side surfaces of the adjacent lattice grooves 3a and 3b corresponds to the pitch of the long pitch periodic structure LP, and the distance Λ2 between the side surfaces of adjacent lattice grooves 2a and 2b corresponds to the pitch of the second short-pitch periodic structure SSP. In the optical resonator structure 10, the direction indicated by the arrow x is a direction orthogonal to lattice grooves, and the length of the first short-pitch structure FSP in the x-direction corresponds to WS1, the length of the long-pitch structure LP in the x-direction corresponds to WL and the length of the second short-pitch structure in the x-direction corresponds to WS2.

In each of the supercell structures, the first short-pitch periodic structure is arranged adjacent to one end of the long-pitch periodic structure, and the second short-pitch periodic structure is arranged adjacent to the other end of the long-pitch periodic structure. The first short-pitch periodic structure may be in contact with one end of the long-pitch periodic structure, and the second short-pitch periodic structure is in contact with the other end of the long-pitch periodic structure.
In each of the supercell structures, at least two of (i) a direction orthogonal to lattice grooves of the first short-pitch periodic structure, (ii) a direction orthogonal to lattice grooves of the long-pitch periodic structure and (iii) a direction orthogonal to lattice grooves of the second short-pitch periodic structure are on a straight line. Directions that lie on a straight line may be (i) and (ii), (i) and (iii), (ii) and (iii), (i), (ii) and (iii). All of (i), (ii) and (iii) may be on a straight line.

In each of the supercell structures, the pitches of the first short-pitch periodic structure and the second short-pitch periodic structure may be the same as or different from each other, for example the same as. The lengths WS1 and WS2 may be the same as or different from each other, for example the same as. In one embodiment of the invention, the pitches of the first short-pitch structure and the second short-pitch structure are same as, and the first short-pitch structure and the second short-pitch structure satisfy W1=W2.

The method of the invention comprises at least one process of (1) to (4) above. The processes conducted in the method of the invention may be part of (1) to (4), or may be all of (1) to (4). Embodiments of the method of the invention include the following (A) to (I).
(A) The method comprising conducting (1).
(B) The method comprising conducting (2).
(C) The method comprising conducting (3).
(D) The method comprising conducting (4).
(E) The method comprising conducting (1) and (2).
(F) The method comprising conducting (1) and (3).
(G) The method comprising conducting (2) and (3).
(H) The method comprising conducting (1), (2) and (3).
(I) In any embodiment of (A) to (H), the method further comprises conducting (4).

In the method of the invention, (WS1 + WS2) / WL is adjusted to be for example 4 or more, for example 10 or more, for example 50 or more, for example 90 or more, for example 150 or more, and for example 800 or more.
In the method of the invention, (WS1 + WS2) is adjusted to be for example 1 μm or more, for example 4 μm or more, for example 10 μm or more, for example 40 μm or more, and for example 200 μm or more.
In the method of the invention, WL is adjusted to be for example 10 μm or less, for example 2 μm or less, and for example 0.6 μm or less.
In the method of the invention, (WS1 + WL + WS2) is for example 2 μm or more, for example 5 μm or more, for example 20 μm or more, for example 50 μm or more, and for example 250 μm or more.
In the method of the invention, the number of supercell structures of the optical resonator structure is for example 4 or more, for example 6 or more, for example 8 or more, and for example 10 or more.

In the method of the invention, the pitches of the first short-pitch periodic structure, the long-pitch periodic structure and the second short-pitch periodic structure may be set to satisfy the Bragg condition represented by the equation (I) described later. In one embodiment of the invention, the first short-pitch periodic structure and the second short-pitch periodic structure are first-order gratings in which m in the equation (I) is 1 each, and the long-pitch periodic structure is a second-order grating in which m in the equation (I) is 2.

Method for designing, evaluating, or producing organic semiconductor laser device
Embodiments of the method of the invention include a method for designing an organic semiconductor laser device, a method for evaluating an organic semiconductor laser device and a method for producing an organic semiconductor laser device.
In the method for designing an organic semiconductor laser device, by conducting at least one of (1) to (4) above, it is possible to design an organic semiconductor laser device that is expected to have low lasing threshold and narrow diffraction angle of laser emission.
In the method for evaluating an organic semiconductor laser device, by evaluating higher an organic semiconductor device that satisfies at least one condition of (1′) (WS1 + WS2) is lengthier, (2′) WL is shorter, (3′) (WS1 + WL + WS2) is lengthier and (4′) the number of the supercell structures is larger, it is possible to select an organic semiconductor device having low lasing threshold and narrow diffraction angle of laser emission among two or more organic semiconductor laser devices.
In the method for producing an organic semiconductor laser device, by conducting at least one of (1) to (4) above, it is possible to produce an organic semiconductor laser device having low lasing threshold and narrow diffraction angle of laser emission.
For the explanations and the conditions used in these methods of the invention, the description in the paragraph "Method for improving Organic Semiconductor Laser Device" above may be referenced.

Program
The program of the invention is a program for conducting the method of the invention. That is, the program of the invention is a program for causing a computer to conduct each process in the method of the invention. For the descriptions for the method of the invention, the description in the paragraph "Method for improving organic semiconductor laser device" and " Method for designing, evaluating, or producing organic semiconductor laser device" above may be referenced.
The program of the invention may be recorded on a recording medium such that it is computer readable. Examples of the recording medium include a magnetic recording medium, an optical recording medium and a semiconductor memory. Specific examples of the recording medium include a flexible disk, a hard disk, an optical disk, a magneto-optical disk, a CD-ROM (Read Only Memory), a CD-R, a DVD-ROM, a magnetic tape, a non-volatile memory card, a ROM, an EEPROM and a silicon disk.

Computer
The computer of the invention is a computer for conducting the method of the invention. That is, the computer of the invention is a computer comprising means for conducting each process in the method of the invention. For the descriptions for the method of the invention, the description in the paragraph "Method for improving organic semiconductor laser device" and " Method for designing, evaluating, or producing organic semiconductor laser device" above may be referenced.
Examples of means that the computer of the invention may comprise include calculation means for calculating the formulas in (1′) and (3′) above, and screening means for selecting an organic semiconductor laser device that fit (1′) to (4′) above among devices based on the calculated values in (1′) and (3′) and the numerical values in (2′) and (4′).

Organic Semiconductor Laser Device
The organic semiconductor laser device of the invention is an organic semiconductor laser device comprising an optical resonator structure and a light amplification layer composed of an organic semiconductor, wherein:
the optical resonator structure has at least one supercell structure which has a first short-pitch periodic structure, a long-pitch periodic structure and a second short-pitch periodic structure,
the first short-pitch periodic structure is arranged adjacent to one end of the long-pitch periodic structure, and the second short-pitch periodic structure is arranged adjacent to the other end of the long-pitch periodic structure,
at least two of (i) a direction orthogonal to lattice grooves of the first short-pitch periodic structure, (ii) a direction orthogonal to lattice grooves of the long-pitch periodic structure and (iii) a direction orthogonal to lattice grooves of the second short-pitch periodic structure are on a straight line, and
the organic semiconductor laser device has at least one of a lengthened (WS1 + WS2), a shortened WL, a lengthened (WS1 + WL + WS2) and two or more supercell structures, wherein WS1 represents a length in a direction orthogonal to lattice grooves of the first short-pitch periodic structure, WS2 represents a length in a direction orthogonal to lattice grooves of the second short-pitch periodic structure, WL represents a length in a direction orthogonal to lattice grooves of the long-pitch periodic structure.
For descriptions of the first short-pitch periodic structure、the long-pitch periodic structure and the second short-pitch structure, exemplified ranges of (WS1 + WS2), WL, (WS1 + WS2) / WL and (WS1 + WL + WS2), the description in the paragraph "Method for improving Organic Semiconductor Laser Device" above may be referenced.

The organic semiconductor laser device of the invention may be an optically pumped organic semiconductor laser device, or may be an electrically pumped organic semiconductor laser device (organic semiconductor laser diode). The optically pumped organic semiconductor laser device has the optical resonator structure and the light amplification layer. The electrically pumped organic semiconductor laser device has a pair of electrodes, the optical resonator structure, an organic layer containing at least the light amplification layer.
The members and the layers of the electrically pumped organic semiconductor laser device will be described below. The descriptions for the optical resonator structure and the light amplification layer may also be applied to the optical resonator structure and the light amplification layer of the optically pumped organic semiconductor laser device.

Electrode
The electrically pumped organic semiconductor laser device of the invention has a pair of electrodes. For light output, one electrode may be transparent. For the electrode, an electrode material generally used in the art may be appropriately selected in consideration of the work function thereof, etc. Electrode materials include, though not limited thereto, Ag, Al, Au, Cu, ITO, etc.

Optical resonator structure
The optical resonator structure has two or more supercell structures above. The number of supercell structures of the optical resonator structure is for example 4 or more, for example 6 or more, for example 8 or more, and for example 10 or more.
The optical resonator structure may have two or more supercell structures arranged so that the directions orthogonal to lattice grooves of the two or more supercell structures are on a straight line. In one embodiment of the invention, WS1, WL and WS2 of the two or more supercell structures are the same. In one embodiment of the invention, the lengths in the directions orthogonal to lattice grooves of the two or more supercell structures are random. An example of the optical resonator structure capable of being used in embodiment with random supercell length above is shown in Fig. 2. The optical resonator structure shown in Fig. 2 has three types of supercell structures SC1, SC2, SC3, with different lengths in directions orthogonal to lattice groove, and the three types of supercell structures are randomly arranged. Where, the lengths of the three types of supercell structures are represented by the following equations.
WL₁ = 30 Λ₁ + 6 Λ₂ + 30 Λ₁
WL₂ = 20 Λ₁ + 5 Λ₂ + 20 Λ₁
WL₃= 8 Λ₁ + 3 Λ₂ + 8 Λ₁
wherein WL₁, WL₂, and WL₃ are each lengths in directions orthogonal to lattice grooves of the three types of supercell structures, Λ₁ is pitch of the first short-pitch periodic structure, and Λ₂ is a pitch of the second short-pitch periodic structure.
Fig. 3 shows the angular dependence of laser emission obtained by simulation of the far-field pattern of laser emission from the laser device having the optical resonator structure shown in Fig. 2. If the length of the supercells is not the same for each cell (random supercell length), it results in no periodicity of the supercell and hence the laser will appear at single angle at 0 degree. This organic semiconductor laser device can act as an array of lasers emitting same wavelength and at single angle.

The first short-pitch periodic structure, the long-pitch periodic structure and the second short-pitch periodic structure of the supercell structures each have grooves with a depth of for example less than 75 nm, and for example from 20 to 70 nm.
In one embodiment of the invention, the first short-pitch periodic structure, the long-pitch periodic structure and the second short-pitch periodic structure have a distributed feedback (DFB) structure. DFB structure is a diffraction grating structure designed to satisfy the Bragg condition of the equation (I).
mλ_Bragg＝2n_effΛ　　　　　　　　　　　　　　（I）
wherein m is the order of diffraction, λ_Bragg is the Bragg resonant wavelength, n_eff is the effective refractive index of the waveguide, and Λ is the grating period (pitch).
DFB structures of the first short-pitch periodic structure, the long-pitch periodic structure and the second short-pitch periodic structure may be selected from the group consisting of first order DFB structure, second order DFB structure, third order DFB structure and even higher order DFB structures. However, in each of the supercell structures, the order of the DFB structure of the long-pitch periodic stricture is greater than the order of the DFB structures of the first short-pitch periodic structure and the second short-pitch periodic structure.

The first short-pitch periodic structure, the long-pitch periodic structure and the second short-pitch periodic structure may be composed of an insulating material. Specific examples of insulating materials include glass, silicon dioxide, and plastics.
In one embodiment of the invention, the first short-pitch periodic structure, the long-pitch periodic structure and the second short-pitch periodic structure are integrally formed of insulating material.
In one embodiment of the invention, the first short-pitch periodic structure, the long-pitch periodic structure and the second short-pitch periodic structure have periodically-arranged ridges composed of an insulating material on an insulating substrate. In this case, the ridges and the insulating substrate may be composed of different insulating materials. For example, the ridges may be composed of silicon dioxide, and the insulating substrate may be composed of a glass substrate. In the periodic structure having the periodically-arranged ridges on the insulating substrate, the surface of the insulating substrate may be exposed at the bottom of the grooves (between adjacent ridges). For the range of the height of the ridges, the range of the depth of the lattice groove above may be referenced.

Organic layer
The organic layer contains at least a light amplification layer composed of an organic semiconductor. The organic layer may be provided on a surface of the optical resonator structure.

Light amplification layer in organic layer
The organic semiconductor used in light amplification layer may be a compound composed of one or more atoms selected from the group consisting of a carbon atom, a hydrogen atom, a nitrogen atom, an oxygen atom, a sulfur atom, a phosphorous atom, and a boron atom. Examples of such compound include a compound composed of one or more atoms selected from a carbon atom, a hydrogen atom, and a nitrogen atom.
The light amplification layer contains at least an organic semiconductor exhibiting laser activity. The "organic semiconductor exhibiting laser activity" referred herein means an organic semiconductor capable of causing laser oscillation by supplying energy from the outside. Hereinafter, the "organic semiconductor exhibiting laser activity" will be referred to as a "laser active material".
An example of the laser active material is a compound having at least one of a stilbene unit, and another example of the laser active material is a compound having at least one of a stilbene unit and at least one of a carbazole unit. The stilbene unit and the carbazole unit may be substituted with a substituent such as an alkyl group or the like, or may be unsubstituted. The organic semiconductor compound may be a non-polymer not having a repeating unit. The molecular weight of the compound may be 1000 or less, for example, it may be 750 or less. Specific examples of the laser active material include 4,4'-bis[(N-carbazole)styryl]biphenyl (BSBCz) (chemical structure in Fig. 4 (d)). The light amplification layer may contain 2 or more kinds of a laser active material. For example, the light amplification layer contains only one kind of a laser active material.
The light amplification layer may consist solely of the laser active material, or may contain other organic semiconductors in addition to the laser active material. An example of other organic semiconductors is an organic semiconductor as a host material. The host material used may be an organic compound that has excited singlet energy and excited triplet energy, at least one of which is higher than those of the laser active material. As a result, the singlet excitons and the triplet excitons generated in the laser active material are capable of being confined in the molecules of the laser active material, thereby lowering lasing threshold. However, there are cases where laser properties are improved even though the singlet excitons and the triplet excitons may not be sufficiently confined, and therefore host materials capable of improving laser properties may be used in the invention without any particular limitation. The host material can be appropriately selected from known host materials and may be an organic semiconductor having a high glass transition temperature.
In the case where the host material is used, the amount of the laser active material in the light amplification layer is for example 0.1% by weight or more, and for example 1% by weight or more, and is for example 50% by weight or less, for example 20% by weight or less, and for example 10% by weight or less.
Stimulated emission light generated by the laser active material is emitted outside as laser light by the action of the optical resonator structure. In one embodiment of the invention, laser light derived the laser active material diffracts by the supercell structures of the optical resonator structure and is emitted as diffracted light to the outside. At this time, the light emitted from the organic semiconductor laser device may include light emitted from the host material. The light derived from the laser active material may be the major component.

Other layers in organic layer
The organic layer may be formed only of a light amplification layer, or may have one or more organic layers in addition to the light amplification layer. Examples of the organic layer include an electron injection layer, a hole injection layer.
The performance of the electrically pumped organic semiconductor laser device tends to be better when the number of the heterointerfaces of the organic layers therein is smaller, and therefore, the number of the organic layers therein is for example 3 or less, for example 2 or less, for example 1. In the case where the electrically pumped organic semiconductor laser device has 2 or more organic layers, for example, the thickness of the light amplification layer is more than 50% of the total thickness of the organic layers, for example more than 60%, and for example more than 70%. When the electrically pumped organic semiconductor laser device has 2 or more organic layers, the total thickness of the organic layers may be, for example, 100 nm or more, 120 run or more, or 170 or more, and may be 370 nm or less, 320 nm or less, or 270 nm or less. The refractive index of the electron injection layer and the hole injection layer may be smaller than the refractive index of the light amplification layer.
In the case where an electron injection layer is provided, a substance facilitating electron injection into the light amplification layer may be made to exist in the electron injection layer. In the case where a hole injection layer is provided, a substance facilitating hole injection into the light amplification layer may be made to exist in the hole injection layer. These substances may be an organic compound or an inorganic substance. For example, the inorganic substance for the electron injection layer includes an alkali metal such as Cs, etc., and the concentration thereof in the electron injection layer containing an organic compound may be, for example, 1% by weight more, or 5% by weight or more, or 10% by weight or more, and may be 40% by weight or less, or 30% by weight or less. The thickness of the electron injection layer may be, for example, 3 nm or more, 10 nm or more, or 30 nm or more, and may be 100 nm or less, 80 nm or less, or 60 nm or less.
The film forming method of the light amplification and other layers of the organic layer are not particularly limited, and each layer of the organic layer may be produced by any of a dry process and a wet process.
The thickness of the entire organic layer including the optical amplification layer is for example 80 to 350 nm, for example 100 to 300 nm, and for example 150 to 250 nm.

Other layers
The organic semiconductor laser device of the invention may be composed only of the optical resonator structure and the organic semiconductor layer, or may further include other layers. Other layers include a transparent protective layer. The transparent protective layer is provided on a side opposite to the optical resonator structure of the organic layer. The transparent protective layer has the function of protecting the organic layer.
A transparent protective layer may be formed of a substantially transparent material. Examples of materials used for the transparent protective layer include a fluorine-containing resin and a sapphire glass. A laminate (fluorine-containing resin/sapphire glass) in which sapphire glass is layered on fluorine-containing resin applied to the surface of the organic layer may be used as the transparent protective layer. As a commercially available resin, for example, CYTOP (AGC Chemicals) may be used.

In the organic semiconductor laser device of the invention, a laser beam may be emitted from the opposite side of the organic layer of the optical resonator structure, or may be emitted from the opposite side of the organic layer of the transparent protective layer.
Since the organic semiconductor laser device of the invention comprises an optical resonator structure having at least one of a lengthened (WS1 + WS2), a shortened WL, a lengthened (WS1 + WL + WS2) and two or more supercell structures, it exhibits a low lasing threshold. Further, in one embodiment of the invention, the organic semiconductor laser device emits a split laser beam with narrow angle difference between the diffraction angles of the diffracted beams. Therefore, the organic semiconductor laser device can be effectively used as a structured lighting device for detecting 3D geometry. In this case, the angle difference between the diffraction angles of two diffracted beams light having the closest emission direction among the two or more types of diffracted beams is 8° or less, for example 7° or less, and for example 6° or less.

Usefulness of Organic Semiconductor Laser Device
As mentioned above, the organic semiconductor laser device of the invention exhibits low oscillation threshold, and narrow diffraction angle of laser emission. Therefore, the organic semiconductor laser device of the present invention is useful as a structured lighting device for detecting 3D geometry, and can be effectively used in a biosensor, a structured optical lighting device, an optical sensing device, and a face recognition device.

Further Detailed Description of The Invention
the invention will be described in more detail below.
The control of laser emission angles in laser devices is essential for many optoelectronic and photonic applications such as optical sensing and displays. In this context, we studied the light diffraction pattern of laser beams in a one-dimensional sampled distributed feedback (1D-DFB) resonator having an organic gain media. The gratings consist of the repetition of supercells having a mixed-order sampled grating in which 1^st-order gratings surround a 2^nd-order grating. The experimental results showed that the diffraction angles of the laser beams are quite diverse depending on the supercell structures. We demonstrate that the interval of the diffraction angle (θ) of the laser beams is inversely proportional to the length of the supercell experimentally and theoretically. By tuning the length of supercells as well as the length of 1^st-order and 2^nd-order regions, the interval θ was tuned from 0.1° to 43° with the different arc emission patterns. With the reduction of θ, i.e., the longer 1^st-order region, a significant decrease in the laser threshold was obtained, resulting in the lowest lasing threshold of 2.5±0.1 μJ/cm² with ~3.5 ns of a long pulse-width excitation source.

The features of the invention will be described more specifically with reference to working examples below.
In this work, we studied the light diffraction pattern and laser threshold from a one-dimensional (1D)-sampled DFB resonator with an organic gain layer. In our recent OSLDs (Organic Semiconductor Laser Diodes) with a mixed-order DFB structure, we observed the light was diffracted into different angles and each angle between the diffracted beams was 10° (We call the angle between the diffracted beams in the rest of the manuscript as “diffraction angle”). The characteristic arc intensified laser emission pattern with each 10° diffraction angle.¹⁴ Although the relationship between the supercell’s length and the diffraction angle is theoretically well established, the experimental verification and the potential effect such as lowering lasing thresholds have not been well investigated. Especially for organic lasers, diffraction angle manipulation for better resolution has not been conducted so far. Therefore, we designed and fabricated various mixed-order sampled DFB structures with different supercell lengths as well as the length of 1^st- and 2^nd-order regions to resolve this angular problem and decrease the laser threshold.

Grating design
The DFB structures used in this study are composed of the repetition of a supercell having a mixed-order grating, i.e., a 2^nd-order grating is sandwiched by 1^st-order gratings at both sides (Fig. 4). The length of the 1^st-order DFB region is varied from 1,632 nm to 27,200 nm. As an organic gain media, a guest:host system of 6 wt%-BSBCz:CBP was employed since it provides the best lasing behavior.¹⁵ Fourier imaging spectroscopy is also used to measure the diffraction angle of the emitted laser beams. In the DFB resonators, the optical feedback is produced due to the coupling between forward and backward propagating waves.¹⁶ This coupling is maximum for a specific wavelength that satisfies the Bragg condition:
mλ_Bragg = 2n_eff Λ (1)
where m is the order of diffraction, λ_Bragg is the Bragg resonant wavelength, n_eff is the effective refractive index of the waveguide, and Λ is the grating period. In the case of 2^nd-order gratings, m is equal to 2, and for the 1^st-order gratings, m is equal to 1. In addition, the light diffraction by the supercell is described by Fraunhofer diffraction law:
nλ₀ = Λ_SC ・ sin θ_m (2)
where n is a diffraction order, λ₀ is the laser emission around the Bragg wavelength, Λ_SC is a supercell length, and θ_m is a diffraction angle. According to this formula, the diffraction angle is inversely proportional to the supercell length. For the design of DFB resonators, the Bragg wavelength was chosen to be 465 nm because the peak wavelength of the amplified spontaneous emission (ASE) spectrum of the BSBCz:CBP film has a peak at 465 nm (Fig. 11).
The DFB resonator is composed of the repetition of supercells. Each supercell is composed of a 2^nd-order grating surrounded by two 1^st-order gratings. The 1^st- and 2^nd-order DFB gratings have one period of 136 and 272 nm, respectively (Fig. 4 (a)). The period length was determined by testing the standard 2^nd-order DFB devices with different period lengths with keeping the same device architectures such as total thickness and the gain media, resulted in the best candidate which demonstrated the lowest optical threshold (Fig. 12 (b)). Then, the 1^st-order period was automatically defined by dividing the 2^nd-order period length by 2. The empirical effective refractive index was characterized as 1.71. Then, we composed three kinds of mixed-order DFBs with 4:12, 4:36, and 4:200 (2^nd-order:1^st-order) ratio with the same number of 2^nd-order periods of 4 (dark blue) in each supercell (Fig. 4 (b)). The first candidate, the 4:12 ratio structure, has been employed in the first OSLD structure, and we decided to use this architecture as a reference. Other candidates have a longer 1^st-order length than that of a 4:12 ratio structure, meaning that the supercell length is extended by the lengthened 1^st-order area. For the specific supercell length, the ratio of 4:12 has 2,720 nm, 4:36 has 5,984 nm, and 4:200 has 28,288 nm, respectively, as shown in Fig. 4(b).

Device fabrication
For an organic semiconductor laser (OSL) device fabrication, we prepared mixed-order DFBs on glass substrates covered with a sputtered 70 nm-thick SiO₂. First, the substrates were cleaned by ultrasonication with acetone and boiled isopropanol successively. Following the solvent cleaning, a UV ozone treatment for 15 min. was applied. To make the SiO₂ surface hydrophobic, hexamethyldisilazane (HDMS) was spin-coated at 4000 rpm for 15 sec. and annealed at 120 ℃ for 2 min. Then, the photoresist solution prepared by mixing both ZEP-520A and ZEP-520A-7 (ZEON) with a 1:2 ratio was spin-coated at 4,500 rpm for 30 sec. and then 300 rpm for 15 sec. on top of the substrate, and annealed at 180 ℃ for 4 min. The thickness of the resultant resist layer was 50 nm. Finally, an electrification dissipating material, Espacer (Showa Denko), was spin-coated at 1500 rpm for 30 sec. and annealed at 80 ℃ for 4 min. Then, DFB grating patterns were depicted on the substrate using an ELS-G100 electron beam lithography system (Elionix). The chip area was 1×1 mm2. After the electron beam exposure, the grating patterns were developed in oxylene solvent for 1 min. at room temperature. The corrugated resist layer was then etched by an RIE-10NR reactive ion etching machine (SAMCO). Here, firstly CHF3 gas with a flow rate of 30 sccm and a power of 70 W was applied for 5 min. After that, the residual part of the resist layer was cleaned by O2 gas with a flow rate of 70 sccm and a power of 100 W for 1 min. The resulting height of the grating was estimated to be 69±5 nm. The grating surface was observed by a scanning electron microscope (JSM-7900F, JEOL) as shown in Fig. 13. Next, on top of the glass/SiO₂ grating, an active layer was fabricated by thermal co-evaporation of 6 wt%-BSBCz as a guest and CBP as a host with a thickness of 200 nm, and the device was stored under vacuum for 24 hrs. to harden the CYTOP layer which was coated on top of the device as a protection layer. The schematic of the OSL structure is shown in Fig. 4 (c).

RESULTS AND DISCUSSION
The lasing properties of OSLs were investigated under pulsed optical pumping with a pump wavelength of 337 nm and a pulse width of ~3.5 ns from an NL100 nitrogen laser (thinkSRS Inc.). The pump beam area was ~ 2.0×10^-3 cm² (Fig. 10). OSLs were excited from the upside of a sapphire cover glass with the perpendicular direction to the substrate surface (0°), and the light emission patterns were recorded from the glass substrate side at 0° using a multichannel spectrophotometer (PMA-
50 from Hamamatsu) (Fig. 7).

Emission diffraction angle measurement
We firstly carried out angular-dependent emission, i.e., the photonic band diagram of the DFB OSLs, to confirm the Fraunhofer diffraction for three grating designs. The photonic band diagrams were measured using a Fourier imaging spectroscopy system (Fig. 8). This measurement system has an objective lens and a Fourier lens which can gather the multiple diffraction orders within an angle θ ranging from -23° to 23°. The details of this experimental setup are described in the Supplementary material. We used an NL100 nitrogen laser for the excitation and a polarizer to separate TE from TM modes. The measured photonic band diagrams of the mixed-order sampled DFBs with 4:12, 4:36, and 4:200 ratios are presented in Fig. 5. These photonic band diagrams show how the wavelength for optimum coupling (Bragg wavelength) varies with angle, mapping out many bands that cross at specific angles. In the case of a simple structure with only a 2^nd-order grating, we observed only two bands that cross each other at 0°, which has been well established in the previous study.¹⁷ Fig. 5 (a)-(c) shows the photonic bands of the OSLs with 4:12, 4:36, and 4:200 ratios, corresponding to the supercell period of 2,720 nm, 5,984 nm, and 28,288 nm, respectively. These spectra showed characteristic spectral and angular narrowing originating from the photonicband structures. Above the threshold, the angular narrowing of the laser beam into the direction perpendicular to the grating occurred, corresponding to the diffracted laser beam. Note that the beam shape in the direction parallel to the grating has a fan shape.¹⁸ Near the lasing threshold, the photonic band diagrams of three OSLs clearly showed multiple bands crossing at different equidistant angles as shown in Fig. 5 (a)-(c). In the angular range -20° < θ < +20°, we can observe that the photonic bands cross at different wavelengths and equidistant angles. Thus, the appearance of additional photonic bands in the OSLs is due to the addition of a second periodicity, i.e., a supercell period, which produces a Fraunhofer diffraction (an example of the photonic band in a single period structure is shown in Fig. 15). The angles between two diffracted beams satisfy the Fraunhofer law (Eq. 2) and at each crossing of the photonic bands, a photonic stop band appeared. At the band edge of this photonic bandgap, the laser oscillation happened due to the high-quality factor at the band edge as reported in the previous literature.¹⁹ We could observe that the angle between two laser beams is inversely proportional to the length of the supercell as predicted by the Fraunhofer law (Eq. 2). Table 1 (No. 4, 5, and 6) shows the excellent agreement between the measured angles and the calculated ones using Fraunhofer law (Eq. 2) for the diffracted laser beams in different structures.

We further fabricated mixed-order sampled DFBs with the 2^nd-order DFB (1 period and 36 periods) in each supercell with different 1^st-order DFB periods by keeping the ratio of 4:12, 4:36, and 4:200. The experimental and calculated angles of diffraction are summarized in Table 1 (No. 1, 2, 3 (1 period) and 7, 8, 9 (36 periods)) and the photonic band diagram is presented in Fig. 16 and 17. From Table 1, by extending the length of the supercells, we could observe the trend of a
narrower angle of the diffraction in each comparison and it converged to the minimum value of 0.1° in the case of No. 9. Here, the supercell length as well as the lengths of the 1^st and the 2^nd-order DFB regions control the diffraction angles. As an example, the ratios of 1:3, 1:9, and 1:50 described in Table 1 (No. 1, 2, and 3) showed highly separated far-field emissions with extremely large diffraction angles (Fig. 16). On the other hand, the ratios of 36:108, 36:324, and 36:1800 described in Table 1 (No. 7, 8, and 9) show highly localized far-field emission with extremely low diffraction angles (Fig. 17).

OSL lasing threshold measurement
From the photonic band diagram measurement, we decided that the ratios of 4:12, 4:36, and 4:200 (No. 4, 5, and 6) are the best candidates in terms of the high-resolution and the broad angular range lasing. Thus, we conducted the lasing threshold measurement with a 0° measurement system. The lasing thresholds were determined from the measured input-output optical power characteristics of OSLs. Fig. 6 (a), (b), and (c) show the emission spectra below and above the threshold for OSLs with the mixed-order sampled DFB resonators with the different ratios of 1^st- and 2^nd-orders. Below the threshold, the photonic stopband width is about 2.86, 3.89, and 4.60 nm for the ratios of 4:12, 4:36, and 4:200, respectively. The center of the photonic stopband locates at 465 nm and is the same for three OSLs. Fig. 6 (d) depicts the variation of the lasing threshold and the photonic stopband width as a function of the length of the 1^st-order region for three different ratios. Interestingly, we could clearly observe that the lasing threshold decreases and the width of the stopband increases, when the length of the 1^st-order grating area increases. Consequently, the OSL with the mixed-order sampled DFB resonator with the ratio of 4:200 exhibited an eight times lower threshold (2.5±0.1 μJ/cm²) and broader stopband than that with the ratio of 4:12 (21.4±1.1 μJ/cm²). Note that we used ~3.5 ns of a relatively long pulse-width excitation source. This decrease in the lasing threshold can be attributed to the enhancement of the planar optical feedback which results from the extended 1^st-order grating length. The amount of the optical feedback is determined by the strength of the backward Bragg scattering which is quantified by the coupling constant. This coupling constant is proportional to the stopband width and is described using the coupled wave theory proposed by Kogelnik and Shank.¹⁶ At one side edge of the stopband, the laser can oscillate and the width of the stopband is a measure of the feedback strength. Consequently, the lasing threshold can be reduced by enhancing the coupling effect, i.e., increasing the coupling constant by increasing the 1^st-order length.
Below the threshold, the emission spectrum displayed additional features which can be ascribed to Bragg dips. These features are clearly observed in the emission of OSLs with the ratios of 4:12 and 4:36. For the OSL with a 4:12 ratio, the features are observed at 450 nm. For the OSL with a 4:36 ratio, the features were observed at 451, 458, 473, and 481 nm, respectively. However, for the OSL with a 4:200 ratio, the spectrum showed somehow very faint features around 460 nm but they are hard to distinguish due to the presence of noise in the emission spectrum. The additional features observed in the 0° emission of the OSLs with the ratios of 4:12 and 4:36 in Fig. 6 (a) and (b) at different wavelengths are also observed in the photonic band diagram in Fig. 5. The emission spectra at the angle axis of 0° are shown on the right side of the photonic band images. For the OSL with a 4:12 ratio, the bands cross at 3 wavelengths of 435 nm, 461 nm, and 503 nm. At the latter two longer wavelengths, the dips are also observed in the 0° emission spectrum due to the overlap of these dips with the emission spectrum. Likewise, for the OSL with a 4:36 ratio, the bands cross at 4 wavelengths of 447, 461, 478, and 498 nm, and the dips are also observed in the 0° emission spectrum due to the overlap of these dips with the emission spectrum. For a 4:200 ratio, the photonic band diagram has high numbers of dips due to the multiple points where the photonic bands cross. These dips constitute additional features that arise from the crossing of the photonic bands at different wavelengths in addition to different angles. The additional dips would have a higher lasing threshold than the main stopband which satisfies the Bragg condition, simply because the gain material, the BSBCz doped film, has the highest gain around the Bragg wavelength, and the possible oscillation wavelength far from this wavelength would have a lower gain. Also, given the trend of diffraction angle, we expect that an even lower diffraction angle and the threshold would be achieved when the supercell length of DFB gets longer. In summary, to obtain a lower threshold, the 1^st-order DFB region should be extended, and the 2^nd-order DFB region should have the best period number and then the control of the diffraction angle is controlled by the length of the supercells.

Conclusions
We designed and studied sampled mixed-order DFB OSLs to control the threshold and the diffraction angle of organic lasers based on Fraunhofer law. First, we controlled the supercell length by changing the ratio of 2^nd-order:1^st-order of sampled mixed-order DFB. In total, 9 different structure DFBs were fabricated and tested. Based on the angular-dependent emission measurement result, the laser diffraction angle was tuned from 0.1° to 43°. This behavior obeys the Fraunhofer law (the diffraction angle is inversely proportional to the supercell length), and the experimental diffraction angles show a good agreement with the calculated ones. Among the 9 DFBs, structures with the ratio of 4:12, 4:36, and 4:200 revealed the broadest angular-range and low diffraction angle emission. Therefore, we chose those 4:12, 4:36, and 4:200 ratio sampled mixed-order DFBs for the further optically pumped lasing threshold measurement. The lasing threshold was decreased by 2.5±0.1 μJ/cm² when the 1^st-order DFB region was increased. The 0° emission spectrum showed that the longer supercell length with the longer 1^st-order region has the broader photonic band gap (i.e. stopband), which suggests the stronger lateral feedback. This result provides useful information on how to control the emission diffraction angle of OSLs/OSLDs with the lower threshold and without the use of a bulky diffractive optical element which enables versatile applications such as biosensors, face recognition technology with 2D and 3D structured light, and ToF systems.

Supplementary Materials
Section 1: Measurement system establishment and device preparation
(a) Lasing property measurement system setup
In this work, two kinds of measurement system were established: a single angular measurement system and Fourier imaging spectroscopy system. A former was designed to measure optical threshold and lasing spectra by perpendicular direction (0 °) light emission from a DFB laser device. A pumping laser source was a NL100 nitrogen laser (thinkSRS, 337 nm of wavelength and 3.5 ns of pulse width) or Nd:YAG laser (355 nm of wavelength and 0.9 ns of pulse width). Three concentration adjustable ND filters were used to minutely control the power of pumping source and draw the optical threshold graph. A rough pumping light was filtered by an aperture to make a clear circle beam shape. Finally, a 355 nm cut filter was put behind the sample and in front of a PMA50 detector to cut the source light which disturbs the detection of emitted light from the device.
In contrast, a later was designed to gather and capture the wide angular dependent photo luminescence (PL) image. A pumping laser source was the same NL100 nitrogen laser with a single angular measurement system. Firstly, the pumping light was chopped into a circle shape, and a lens was used to control the size of the source beam. Then an objectif lens, a Fourier lens, and a tube lens were put to gather the dispersive wide emission from the DFB device and deliver it into a Shamrock500i spectrometer (Andor Technology). A UV cut filter was put to cut the nitrogen pumping laser, then finally a polarizer was put to filter into 0°or 90° of output laser. In this research, the polarizer was basically set to 0°filtration and the secondary 90°polarization whose intensity was very weak was removed in the images. For acquisition setting, 0.2 second of exposure time was applied.

(b) Pumping laser source profile
The beam shape of a pumping source at the sample position was captured by a WinCamD-LCM CCD camera (Opto Science) to determine the pumping area on the DFB. In this research, the size of nitrogen laser and Nd:YAG laser were measured. The figures below show top view and diagonal view images, and two profiles of x- and y- axis marked on the top view image. Each profile was approximated by Gaussian fit, and its 13.5% of peak was regarded as a standard to determine the width of profiles. Both kinds of laser source had an elliptical beam shape and each axis was controlled not to go more than 1000 nm which is a width of DFBs size designed for this work.

(c) Absorption, PL and ASE of 6wt%BSBCz:CBP thin film
For the consistent optical properties, the thin film was fabricated by thermal co-evaporation system. The procedure involves parameters such as film thickness, UV-vis absorption (Abs) spectra, photo luminescence (PL) spectra, amplified spontaneous emission (ASE) spectra, and photo luminescence quantum yield (PLQY). First of all, the film thickness was measured by Dektak XT stylus profiler (BRUKER) and it was 202±2 nm. For the doping rate estimation, the peak wavelength of ASE spectra was employed since the wavelength shifts according to the molecular weight ratio of host and guest materials. Second, Abs spectra and PL spectra was recorded by LAMDA950 (PerkinElmer) and FluoroMax-4 (Horiba) respectively (Fig. 11). Third, the estimated ASE wavelength of 6 wt% was 465 nm, and this parameter was measured by PMA50 (Hamamatsu Photonics). Finally, a PLQY of the film was measured by Quantaurus-QY (Hamamatsu Photonics) and it was 93% at 330 nm of excitation wavelength.

(d) Period optimization of the mixed-order DFB resonator
For the simple comparison, only second-order DFB was utilized for optimizing the period length of grating. 5 candidates of second-order period length were chosen: 260 nm, 264 nm, 272 nm, 276 nm, and 280 nm. All candidates had the same 0.5 of duty cycle. To determine the best one, all second-order DFB devices with the evaporated BSBCz:CBP (6 wt%, 200 nm thickness) film on the DFB were fabricated and their lasing spectra and threshold were measured. Note that Nd:YAG laser pumping source was used for this experiment. Fig. 12(a) shows lasing spectrum of the devices with each DFB candidate plus an ASE spectra of the BSBCz:CBP film without DFB. These five lasing spectrum showed all 0.14 to 0.16 nm of extremely narrow full width at half maximum (FWHM), compared to ASE spectra which had 7.20 nm of broad FWHM. Among the candidates, a device with 272 nm of second-order period length (Λ) was expected to show the lowest optical threshold since it had the largest overlap with the ASE spectra, which means the best gain effect in the DFB resonator was suggested. This suggestion was verified by measuring and comparing the lasing threshold showed in Fig. 12(b). Therefore, the supercell lengths of the sampled mixed-order DFBs in this research were decided based on the optimized periods lengths, i.e. 272 nm of second-order and 136 nm of first-order.

(e) SEM images of DFB structures
In order to compare the structural difference, the period lengths of first-order and second-order were fixed as 136 nm and 272 nm respectively. Then 3 different structures which have different supercell length with the identical 4 periods of second-order gratings in each supercell were taken by Scanning electron microscope (SEM). 40 mA power gold sputtering for 60 seconds was preceded to increase conductivity of the SiO₂ grating surface. Fig. 13(a, b, c) shows the geometry of 1:3, 1:9 and 1:50 ratios sampled mixed-order grating, respectively. The additional sampled mixed-order DFBs (with 1 and 36 periods of second DFB region and different ratios (1:3, 1:9, and 1:50) mentioned on the final part of the article were fabricated on the same day and with the same condition.

Section 2: Details of the main experiment
(a) Emission spectra measurement at 0°
Every output emission was recorded by a single angular measurement system (Fig. 7) with PMA software published by Hamamatsu Photonics. The software setting parameters for data acquisition included 2 factors: 200 ms of exposure time, and 5 times of averaging for each frame. On the first stage, the pumping laser beam size on the position of a sample will be measured was captured as described in Section 1(b). The beam area was then calculated in cm² scale, by a formula of the area of ellipse. Then the sample was located right on the beam size captured position and wavelength-power (counts) measurement was conducted. During the measuring, the pumping laser power was increased until the output power counting peak saturation, by gradually switching the concentration of ND filters. Each frame captured with separate concentration of ND filter was then recorded. Finally, the sample was replaced by a nanojoule-meter (Ophir Photonics) to record all pumping powers used (in μJ scale).
For the next stage, every captured data was collected and gathered into a graph in order to express the lasing threshold (Fig. 14). A graph includes 3 factors: excitation intensity (x-axis), normalized emission intensity (y-axis), and FWHM (secondary y-axis). First, every excitation intensity point was expressed by following formula S1:

where a pumping power (μJ) is E, a calculated pumping beam area (cm²) is A, and an absorbance coefficient is c. The coefficient c was expressed by 1-10^-Abs, where “Abs” is referred by a previously measured absorbance of the gain film by LAMDA950 (PerkinElmer). A specific Abs parameter refers to an excitation wavelength of the pumping laser source, i.e. 337 nm in case of a nitrogen laser source (NL100, thinkSRS), and 355 nm in case of a Nd:YAG laser source (maker). In addition, the normalized emission intensity was summarized by the counts of emission power. And finally FWHM was noted on the right side y-axis. All graphs were expressed by a log-log scale, and a single crossed point formed by two approximated straight lines based on the trend of normalized emission intensities was defined as the lasing threshold point. For verification of the reproducibility of the threshold value, 3 samples of each DFB structure (4 periods of second order DFB region and 1:3, 1:9, and 1:50 ratios) were fabricated and their laser devices were tested simultaneously, at the same condition.

(b) Fourier imaging spectroscopy of sampled mixed-order DFB lasers with only 1 or 36 second-order gratings in each supercell
In addition to the main experiment with 4 periods of second order DFB regions and different ratios ratio mixed order DFBs, DFB OSLs with 1 and 36 periods of second order DFB regions and different ratios (1:3 1:9 and 1:50) were also fabricated and characterized. Fig. 15 and Fig. 16 show the photonic band diagrams and both theoretical and experimental diffraction angles. Note that the secondary peaks (red dash line area) in the above threshold images of Fig. 15(a) and 15(b) are noise.
For comparison, we fabricated and measured 2^nd order DFB OSL. Fig. 15 shows the photonic bad diagram of the OSLs.

By using the method of the invention, the lasing threshold of an organic semiconductor laser device can be lowered and the diffraction angle of the laser emission of an organic semiconductor laser device can be narrowed. Therefore, the organic semiconductor device improved by the method of the present invention can be effectively used as a structured lighting device for detecting a three-dimensional shape. Accordingly, the invention has high industrial applicability.
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Claims

A method for improving an organic semiconductor laser device comprising an optical resonator structure and a light amplification layer composed of an organic semiconductor, wherein:
the optical resonator structure has at least one supercell structure which has a first short-pitch periodic structure, a long-pitch periodic structure and a second short-pitch periodic structure,
the first short-pitch periodic structure is arranged adjacent to one end of the long-pitch periodic structure, and the second short-pitch periodic structure is arranged adjacent to the other end of the long-pitch periodic structure,
at least two of (i) a direction orthogonal to lattice grooves of the first short-pitch periodic structure, (ii) a direction orthogonal to lattice grooves of the long-pitch periodic structure and (iii) a direction orthogonal to lattice grooves of the second short-pitch periodic structure are on a straight line, and
the method comprises at least one of:
(1) lengthening (WS1 + WS2),
(2) shortening WL,
(3) lengthening (WS1 + WL + WS2), and
(4) repeating the supercell structure,
wherein WS1 represents a length in a direction orthogonal to lattice grooves of the first short-pitch periodic structure, WS2 represents a length in a direction orthogonal to lattice grooves of the second short-pitch periodic structure, WL represents a length in a direction orthogonal to lattice grooves of the long-pitch periodic structure.
The method according to Claim 1, conducting (1).
The method according to Claim 1, conducting (2).
The method according to Claim 1, conducting (3).
The method according to Claim 1, conducting (4).
The method according to Claim 1, conducting (1) and (2).
The method according to Claim 1, conducting (1) and (3).
The method according to Claim 1, conducting (2) and (3).
The method according to Claim 1, conducting (1), (2) and (3).
The method according to Claim 6, further conducting (4).
The method according to Claim 1, adjusting (WS1 + WS2) / WL to be 4 or more.
The method according to Claim 1, adjusting (WS1 + WS2) to be 1 μm or more.
The method according to Claim 1, adjusting WL to be 10 μm or less.
The method according to Claim 1, adjusting (WS1 + WL + WS2) to be 2 μm or more.
The method according to Claim 1, satisfying WS1=WS2.
The method according to Claim 1, wherein all of (i) a direction orthogonal to lattice grooves of the first short-pitch periodic structure, (ii) a direction orthogonal to lattice grooves of the long-pitch periodic structure and (iii) a direction orthogonal to lattice grooves of the second short-pitch periodic structure are on a straight line.
The method according to Claim 1, wherein the first short-pitch periodic structure is in contact with one end of the long-pitch periodic structure, and the second short-pitch periodic structure is in contact with the other end of the long-pitch periodic structure.
The method according to Claim 1, wherein the periodic structure is a grating composed of ridges and grooves.
The method according to Claim 18, wherein the first short-pitch periodic structure and the second short-pitch periodic structure are first-order gratings, and the long-pitch periodic structure is a second-order grating.
The method according to Claim 1, wherein the method is for lowering lasing threshold.
The method according to Claim 1, wherein the method is for narrowing diffraction angle of laser emission.
The method according to Claim 1, wherein the method is for lowering lasing threshold and narrowing diffraction angle of laser emission.
The method according to Claim 1, wherein the method is for designing an organic semiconductor laser device.
The method according to Claim 1, wherein the method is for evaluating an organic semiconductor laser device.
The method according to Claim 1, wherein the method is for producing an organic semiconductor laser device.
A program for conducting the method of Claim 1.
A computer for conducting the method of Claim 1.
An organic semiconductor laser device produced by the method of Claim 25.
An organic semiconductor laser device comprising an optical resonator structure and a light amplification layer composed of an organic semiconductor, wherein:
the optical resonator structure has at least one supercell structure which has a first short-pitch periodic structure, a long-pitch periodic structure and a second short-pitch periodic structure,
the first short-pitch periodic structure is arranged adjacent to one end of the long-pitch periodic structure, and the second short-pitch periodic structure is arranged adjacent to the other end of the long-pitch periodic structure,
at least two of (i) a direction orthogonal to lattice grooves of the first short-pitch periodic structure, (ii) a direction orthogonal to lattice grooves of the long-pitch periodic structure and (iii) a direction orthogonal to lattice grooves of the second short-pitch periodic structure are on a straight line, and
the organic semiconductor laser device has at least one of a lengthened (WS1 + WS2), a shortened WL, a lengthened (WS1 + WL + WS2) and two or more supercell structures, wherein WS1 represents a length in a direction orthogonal to lattice grooves of the first short-pitch periodic structure, WS2 represents a length in a direction orthogonal to lattice grooves of the second short-pitch periodic structure, WL represents a length in a direction orthogonal to lattice grooves of the long-pitch periodic structure.
The organic semiconductor laser device according to Claim 28, wherein the optical resonator structure has two or more supercell structures arranged so that directions orthogonal to lattice grooves of the two or more supercell structures are on a straight line.
The organic semiconductor laser device according to Claim 30, wherein WS1, WL and WS2 of the two or more supercell structures are the same.
The organic semiconductor laser device according to Claim 30, wherein the lengths in the directions orthogonal to lattice grooves of the two or more supercell structures are random.
The organic semiconductor laser device according to Claim 30, wherein the optical resonator structure has 10 or more supercell structures.
The organic semiconductor laser device according to Claim 28, wherein the first short-pitch periodic structure, the long-pitch periodic structure, and the second short-pitch periodic structure have grooves with a depth of less than 75 nm.
The organic semiconductor laser device according to Claim 28, wherein the first short-pitch periodic structure, the long-pitch periodic structure, and the second short-pitch periodic structure have a distributed feedback (DFB) structure.
The organic semiconductor laser device according to Claim 35, wherein each distributed feedback (DFB) structure is selected from the group consisting of first order DFB structure, second order DFB structure, third order DFB structure and even higher order DFB structures.
The organic semiconductor laser device according to Claim 28, wherein the first short-pitch periodic structure, the long-pitch periodic structure, and the second short-pitch periodic structure are composed of an insulating material.
The organic semiconductor laser device according to Claim 28, wherein the first short-pitch periodic structure, the long-pitch periodic structure, and the second short-pitch periodic structure have periodically-arranged ridges composed of an insulating material on an insulating substrate.
The organic semiconductor laser device according to Claim 38, wherein the ridges and the insulating substrate are composed of different insulating materials.
The organic semiconductor laser device according to Claim 38, wherein the ridges are composed of silicon dioxide, and the insulating substrate is composed of a glass substrate.
The organic semiconductor laser device according to Claim 38, wherein the surface of the insulating substrate is exposed at the bottom of the grooves.
The organic semiconductor laser device according to Claim 28, further comprising an organic layer on a surface of the optical resonator structure.
The organic semiconductor laser device according to Claim 42, further comprising a transparent protective layer on a side opposite to the optical resonator structure of the organic layer.
The organic semiconductor laser device according to Claim 42, emitting a laser beam from the opposite side of the organic layer of the optical resonator structure.
The organic semiconductor laser device according to Claim 43, emitting a laser beam from the opposite side of the organic layer of the transparent protective layer.
The organic semiconductor laser device according to Claim 28, emitting two or more types of diffracted light having different diffraction angles.
The organic semiconductor laser device according to Claim 46, wherein the angle difference between the diffraction angles of diffracted light having the closest emission direction among the two or more types of diffracted light is 8° or less.
The organic semiconductor laser device according to Claim 28, wherein the organic layer contains an organic compound having at least one stilbene unit.
The organic semiconductor laser device according to Claim 28, wherein the organic layer contains 4,4 '- bis [ (N-carbazole) styryl ] biphenyl (BSBCz).
The organic semiconductor laser device according to Claim 28, wherein the organic layer has a thickness of 80 to 350 nm.
A device selected from the group consisting of a biosensor, a structured optical lighting device, an optical sensing device, and a face recognition device comprising the organic semiconductor laser device of Claim 28.